EQUIDAE

equidae, the family of perissodactyle ungulate mammals typified by the horse (_equus caballus_); see horse. according to the older classification this family was taken to include only the forms with tall-crowned teeth, more or less closely allied to the typical genus _equus_. there is, however, such an almost complete graduation from the former to earlier and more primitive mammals with short-crowned cheek-teeth, at one time included in the family _lophiodontidae_ (see perissodactyla), that it has now become a very general practice to include the whole "phylum" in the family _equidae_. the _equidae_, in this extended sense, together with the extinct _palaeotheriidae_, are indeed now regarded as forming one of four main groups into which the perissodactyla are divided, the other groups being the tapiroidea, rhinocerotoidea and titanotheriide. for the horse-group the name hippoidea is employed. all four groups were closely connected in the lower eocene, so that exact definition is almost impossible. in the hippoidea there is generally the full series of 44 teeth, but the first premolar is often deciduous or wanting in the lower or in both jaws. the incisors are chisel-shaped, and the canines tend to become isolated so as in the now specialized forms to occupy nearly the middle of a longer or shorter gap between the incisors and premolars. in the upper molars the two outer columns of the primitive tubercular molar coalesce to form an outer wall, from which proceed two crescentic transverse crests; the connexion between the crests and the wall being imperfect or slight, and the crests themselves sometimes tubercular. each of the lower molars carries two crescentic ridges. the number of toes ranges from four to one in the fore-foot, and from three to one in the hind-foot. the paroccipital, postglenoid and post-tympanic processes of the skull are large, and the latter always distinct. normally there are no traces of horn-cores. the calcaneum lacks the facet for the fibula found in the titanotheroidea. in the earlier _equidae_ the teeth were short-crowned, with the premolars simpler than the molars; but there is a gradual tendency to an increase in the height of the crowns of the teeth, accompanied by increasing complexity of structure and the filling up of the hollows with cement. similarly the gap on each side of the canine tooth in each jaw continues to increase in length; while in all the later forms the orbit is surrounded by a ring of bone. a third modification is the increasing length of limb (as well as in general bodily size), accompanied by a gradual reduction in the number of toes from three or four to one. [illustration: fig. 1.--a, side view of second upper molar tooth of _anchitherium_ (brachyodont form); b, corresponding tooth of horse (hypsidont form).] all the existing members of the family, such as the domesticated horse (_equus caballus_) and its wild or half-wild relatives, the asses and the zebras, are included in the typical genus. in all these the crowns of the cheek-teeth are very tall (fig. 1, b) and only develop roots late in life; while their grinding-surfaces (fig. 2, b and c) are very complicated and have all the hollows filled with cement. the summits of the incisors are infolded, producing, when partially worn, the "mark." in the skull the orbit is surrounded by bone, and there is no distinct depression in front of the same. each limb terminates in one large toe; the lateral digits being represented by the splint-bones, corresponding to the lateral metacarpals and metatarsals of _hipparion_. not unfrequently, however, the lower ends of the splint-bones carry a small expansion, representing the phalanges. remains of horses indistinguishable from _e. caballus_ occur in the pleistocene deposits of europe and asia; and it is from them that the dun-coloured small horses of northern europe and asia are probably derived. the ancestor of these pleistocene horses is probably _e. stenonis_, of the upper pliocene of europe, which has a small depression in front of the orbit, while the skull is relatively larger, the feet are rather shorter, and the splint-bones somewhat more developed. in india a nearly allied species (_e. sivalensis_), occurs in the lower pliocene, and may have been the ancestor of the arab stock, which shows traces of the depression in front of the orbit characteristic of the earlier forms. in north america species of _equus_ occur in the pleistocene and from that continent others reached south america during the same epoch. in the latter country occurs _hippidium_, in which the cheek-teeth are shorter and simpler, and the nasal bones very long and slender, with elongated slits at the side. the limbs, especially the cannon-bones, are relatively short, and the splint-bones large. the allied argentine _onohippidium_, which is also pleistocene, has still longer nasal bones and slits, and a deep double cavity in front of the orbit, part of which probably contained a gland. _onohippidium_ is certainly off the direct line of descent of the modern horses, and, on account of the length of the nasals and their slits, the same probably holds good for _hippidium_. [illustration: fig. 2.--a, grinding surface of unworn right upper molar tooth of _anchitherium_; b, corresponding surface of unworn molar of young horse; c, the same tooth after it has been some time in use. the uncoloured portions are the dentine or ivory, the shaded parts the cement filling the cavities and surrounding the exterior. the black line separating these two structures is the enamel or hardest constituent of the tooth.] species from the pliocene of texas and the upper miocene (loup fork) of oregon were at one time assigned to _hippidium_, but this is incorrect, that genus being exclusively south american. the name _pliohippus_ has been applied to species from the same two formations on the supposition that the foot-structure was similar to that of _hippidium_, but mr j.w. gidley is of opinion that the lateral digits may have been fully developed. apparently there is here some gap in the line of descent of the horse, and it may be suggested that the evolution took place, not as commonly supposed, in north america, but in eastern central asia, of which the palaeontology is practically unknown; some support is given to this theory by the fact that the earliest species with which we are acquainted occur in northern india. [illustration: fig. 3.--successive stages of modification of the left fore-feet of extinct forms of horse-like animals, showing gradual reduction of the outer and enlargement of the middle toe (iii). a, _hyracotherium_ (eocene). b, _mesohippus_ (oligocene). c, _anchitherium_ (miocene). d, _hipparion_ (pliocene). e, _equus_ (pleistocene).] be this as it may, the next north american representatives of the family constitute the genera _protohippus_ and _merychippus_ of the miocene, in both of which the lateral digits are fully developed and terminate in small though perfect hoofs. in both the cheek-teeth have moderately tall crowns, and in the first named of the two those of the milk-series are nearly similar to their permanent successors. in _merychippus_, on the other hand, the milk-molars have short crowns, without any cement in the hollows, thus resembling the permanent molars of the under-mentioned genus _anchitherium_. from the well-known _hipparion_, or _hippotherium_, typically from the lower pliocene of europe, but also occurring in the corresponding formation in north africa, persia, india and china, and represented in the upper miocene loup fork beds of the united states by species which it has been proposed to separate generically as _neohipparion_, we reach small horses which are now generally regarded as a lateral offshoot from the _merychippus_ type. the cheek-teeth, which have crowns of moderate height, differ from those of all the foregoing in that the postero-internal pillar (the projection on the right-hand top corner of c in fig. 2) is isolated in place of being attached by a narrow neck to the adjacent crescent. the skull, which is relatively short, has a large depression in front of the orbit, commonly supposed to have contained a gland, but this may be doubtful. in the typical, and also in the north american forms these were complete, although small, lateral toes in both feet (fig. 3, d), but it is possible that in _h. antilopinum_ of india the lateral toes had disappeared. if this be so, we have the development of a monodactyle foot in this genus independently of _equus_. the foregoing genera constitute the subfamily _equinae_, or the _equidae_ as restricted by the older writers. in all the dentition is of the hypsodont type, with the hollows of the cheek-teeth filled by cement, the premolars molariform, and the first small and generally deciduous. the orbit is surrounded by a bony ring; the ulna and radius in the fore, and the tibia and fibula in the hind-limb are united, and the feet are of the types described above. between this subfamily and the second subfamily, _hyracotheriinae_, a partial connexion is formed by the north american upper miocene genera _desmatippus_ and _anchippus_ or _parahippus_. the characteristics of the group will be gathered from the remarks on the leading genera; but it may be mentioned that the orbit is open behind, the cheek-teeth are short-crowned and without cement (fig. 1, a), the gap between the canine and the outermost incisor is short, the bones of the middle part of the leg are separate, and there are at least three toes to each foot. the longest-known genus and the one containing the largest species is _anchitherium_, typically from the middle miocene of europe, but also represented by one species from the upper miocene of north america. the european _a. aurelianense_ was of the size of an ordinary donkey. the cheek-teeth are of the type shown in a of figs. 1 and 2; the premolars, with the exception of the small first one, being molar-like; and the lateral toes (fig. 3, c) were to some extent functional. the summits of the incisors were infolded to a small extent. nearly allied is the american _mesohippus_, ranging from the lower miocene to the lower oligocene of the united states, of which the earliest species stood only about 18 in. at the shoulder. the incisors were scarcely, if at all, infolded, and there is a rudiment of the fifth metacarpal (fig. 3, b). by some writers all the species of _mesohippus_ are included in the genus _miohippus_, but others consider that the two genera are distinct. _mesohippus_ and _miohippus_ are connected with the earliest and most primitive mammal which it is possible to include in the family _equidae_ by means of _epihippus_ of the uinta or upper eocene of north america, and _pachynolophus_, or _orohippus_, of the middle and lower eocene of both halves of the northern hemisphere. the final stage, or rather the initial stage, in the series is presented by _hyracotherium_ (_protorohippus_), a mammal no larger than a fox, common to the lower eocene of europe and north america. the general characteristics of this progenitor of the horses are those given above as distinctive of the group. the cheek-teeth are, however, much simpler than those of _anchitherium_; the transverse crests of the upper molars not being fully connected with the outer wall, while the premolars in the upper jaw are triangular, and thus unlike the molars. the incisors are small and the canines scarcely enlarged; the latter having a gap on each side in the lower, but only one on their hinder aspect in the upper jaw. the fore-feet have four complete toes (fig. 3, a), but there are only three hind-toes, with a rudiment of the fifth metatarsal. the vertebrae are simpler in structure than in _equus_. from _hyracotherium_, which is closely related to the eocene representatives of the ancestral stocks of the other three branches of the perissodactyla, the transition is easy to _phenacodus_, the representative of the common ancestor of all the ungulata. see also h.f. osborn, "new oligocene horses," _bull. amer. mus._ vol. xx. p. 167 (1904); j.w. gidley, _proper generic names of miocene horses_, p. 191; and the article palaeontology. (r. l.*) equilibrium (from the lat. _aequus_, equal, and _libra_, a balance), a condition of equal balance between opposite or counteracting forces. by the "sense of equilibrium" is meant the sense, or sensations, by which we have a feeling of security in standing, walking, and indeed in all the movements by which the body is carried through space. such a feeling of security is necessary both for maintaining any posture, such as standing, or for performing any movement. if this feeling is absent or uncertain, or if there are contradictory sensations, then definite muscular movements are inefficiently or irregularly performed, and the body may stagger or fall. when we stand erect on a firm surface, like a floor, there is a feeling of resistance, due to nervous impulses reaching the brain from the soles of the feet and from the muscles of the limbs and trunk. in walking or running, these feelings of resistance seem to precede and guide the muscular movements necessary for the next step. if these are absent or perverted or deficient, as is the case in the disease known as locomotor ataxia, then, although there is no loss of the power of voluntary movement, the patient staggers in walking, especially if he is not allowed to look at his feet, or if he is blind-folded. he misses the guiding sensations that come from the limbs; and with a feeling that he is walking on a soft substance, offering little or no resistance, he staggers, and his muscular movements become irregular. such a condition maybe artificially brought about by washing the soles of the feet with chloroform or ether. and it has been observed to exist partially after extensive destruction of the skin of the soles of the feet by burns or scalds. this shows that tactile impulses from the skin take a share in generating the guiding sensation. in the disease above mentioned, however, tactile impressions may be nearly normal, but the guiding sensation is weak and inefficient, owing to the absence of impulses from the muscles. the disease is known to depend on morbid changes in the posterior columns of the spinal cord, by which impulses are not freely transmitted upwards to the brain. these facts point to the existence of impulses coming from the muscles and tendons. it is now known that there exist peculiar spindles, in muscle, and rosettes or coils or loops of nerve fibres in close proximity to tendons. these are the end organs of the sense. the transmission of impulses gives rise to the _muscular sense_, and the guiding sensation which precedes co-ordinated muscular movements depends on these impulses. thus from the limbs streams of nervous impulses pass to the sensorium from the skin and from muscles and tendons; these may or may not arouse consciousness, but they guide or evoke muscular movements of a co-ordinated character, more especially of the limbs. in animals whose limbs are not adapted for delicate touch nor for the performance of complicated movements, such as some mammals and birds and fishes, the guiding sensations depend largely on the sense of vision. this sense in man, instead of assisting, sometimes disturbs the guiding sensation. it is true that in locomotor ataxia visual sensations may take the place of the tactile and muscular sensations that are inefficient, and the man can walk without staggering if he is allowed to look at the floor, and especially if he is guided by transverse straight lines. on the other hand, the acrobat on the wire-rope dare not trust his visual sensations in the maintenance of his equilibrium. he keeps his eyes fixed on one point instead of allowing them to wander to objects below him, and his muscular movements are regulated by the impulses that come from the skin and muscles of his limbs. the feeling of insecurity probably arises from a conception of height, and also from the knowledge that by no muscular movements can a man avoid a catastrophe if he should fall. a bird, on the other hand, depends largely on visual impressions, and it knows by experience that if launched into the air from a height it can fly. here, probably, is an explanation of the large size of the eyes of birds. cover the head, as in hooding a falcon, and the bird seems to be deprived of the power of voluntary movement. little effect will be produced if we attempt to restrain the movements of a cat by covering its eyes. a fish also is deprived of the power of motion if its eyes are covered. but both in the bird and in the fish tactile and muscular impressions, especially the latter, come into play in the mechanism of equilibrium. in flight the large-winged birds, especially in soaring, can feel the most delicate wind-pressures, both as regards direction and force, and they adapt the position of their body so as to catch the pressure at the most efficient angle. the same is true of the fish, especially of the flat-fishes. in mammals the sense of equilibrium depends, then, on streams of tactile, muscular and visual impressions pouring in on the sensorium, and calling forth appropriate muscular movements. it has also been suggested that impulses coming from the abdominal viscera may take part in the mechanism. the presence in the mesentery of felines (cats, &c.) of large numbers of pacinian corpuscles, which are believed to be modified tactile bodies, favours this supposition. such animals are remarkable for the delicacy of such muscular movements, as balancing and leaping. there is another channel by which nervous impulses reach the sensorium and play their part in the sense of equilibrium, namely, from the semicircular canals, a portion of the internal ear. it is pointed out in the article hearing that the appreciation of sound is in reality an appreciation of variations of pressure. the labyrinth consists of the vestibule, the cochlea and the semicircular canals. the cochlea receives the sound-waves (variations of pressure) that constitute musical tones. this it accomplishes by the structures in the ductus cochlearis. in the vestibule we find two sacs, the saccule next to and communicating with the ductus cochlearis, and the utricle communicating with the semicircular canals. the base of the stapes communicates pressures to the utricle. the membranous portion of the semicircular canals consists of a tube, dilated at one end into a swelling or pouch, termed the ampulla, and each end communicates freely with the utricle. on the posterior wall of both the saccule and of the utricle there is a ridge, termed in each case the macula acustica, bearing a highly specialized epithelium. a similar structure exists in each ampulla. this would suggest that all three structures have to do with hearing; but, on the other hand, there is experimental evidence that the utricle and the canals may transmit impressions that have to do with equilibrium. pressure of the base of the stapes is exerted on the utricle. this will compress the fluid in that cavity, and tend to drive the fluid into the semicircular canals that communicate with that cavity by five openings. each canal is surrounded by a thin layer of perilymph, so that it may yield a little to this pressure, and exert a pull or pressure on the nerve-endings in each ampulla. thus impulses may be generated in the nerves of the ampullae. the three semicircular canals lie in the three directions in space, and it has been suggested that they have to do with our appreciation of the direction of sound. but our appreciation of sound is very inaccurate: we look with the eyes for the source of a sound, and instinctively direct the ears or the head, or both, in the direction from which the sound appears to proceed. but the relationship of the canals on the two sides must have a physiological significance. thus (1) the six canals are parallel, two and two; or (2) the two horizontal canals are in the same plane, while the superior canal on one side is nearly parallel with the posterior canal of the other. these facts point to the two sets of canals and ampullae acting as one organ, in a manner analogous to the action of two retinae for single vision. we have next to consider how the canals may possibly act in connexion with the sense of equilibrium. in 1820 j. purkinje studied the vertigo that follows rapid rotation of the body in the erect position on a vertical axis. on stopping the rotation there is a sense of rotation in the opposite direction, and this may occur even when the eyes are closed. purkinje noticed that the position of the imaginary axis of rotation depends on the axis around which the head revolves. in 1828 m.j.p. flourens discovered that injury to the canals causes disturbance to the equilibrium and loss of co-ordination, and that sections of the canals produce a rotatory movement of a kind corresponding to the canal that had been divided. thus division of a membranous canal causes rotatory movements round an axis at right angles to the plane of the divided canal. the body of the animal always moves in the direction of the cut canal. many other observers have corroborated these experiments. f. goltz was the first who formulated the conditions necessary for equilibration. he put the matter thus:--(1) a central co-ordinating organ--in the brain; (2) centripetal fibres, with their peripheral terminations--in the ampullae; and (3) centrifugal fibres, with their terminal organs--in the muscular mechanisms. a lesion of any one of these portions of the mechanism causes loss or impairment of balancing. cyon also investigated the subject, and concluded:--(1) to maintain equilibrium, we must have an accurate notion of the position of the head in space; (2) the function of the semicircular canals is to communicate impressions that give a representation of this position--each canal having a relation to one of the dimensions of space; (3) disturbance of equilibrium follows section; (4) involuntary movements following section are due to abnormal excitations; (5) abnormal movements occurring a few days after the operation are caused by irritation of the cerebellum. on theoretical considerations of a physical character, e. mach, crum-brown and breuer have advanced theories based on the idea of the canals being organs for sensations of acceleration of movement, or for the sense of rotation. mach first pointed out that purkinje's phenomena, already alluded to, were in all probability related to the semicircular canals. "he showed that when the body is moved in space, in a straight line, we are not conscious of the velocity of motion, but of variations in this velocity. similarly, if a body is rotated round a vertical axis, we perceive only angular acceleration and not angular velocity. the sensations produced by angular acceleration last longer than the acceleration itself, and the position of the head during the movements enables us to determine direction." both mach and goltz state that varying pressures of the fluid in the canals produced by angular rotation produce sensations of movement (always in a direction opposite to the rotation of the body), and that these, in turn, cause the vertigo of purkinje and the phenomena of flourens. mach, crum-brown and breuer advance hydrodynamical theories in which they assume that the fluids move in the canals. goltz, on the other hand, supports a hydrostatical theory in which he assumes that the phenomena can be accounted for by varying pressures. crum-brown differs from mach and breuer as follows:--(1) in attributing movement or variation of pressure not merely to the endolymph, but also to the walls of the membranous canals and to the surrounding perilymph; and (2) in regarding the two labyrinths as one organ, all the six canals being required to form a true conception of the rotating motion of the head. he sums up the matter thus: "we have two ways in which a relative motion can occur between the endolymph and the walls of the cavity containing it--(1) when the head begins to move, here the walls leave the fluid behind; (2) when the head stops, here the fluid flows on. in both cases the sensation of rotation is felt. in the first this sensation corresponds to a real rotation, in the second it does not, but in both it corresponds to a real acceleration (positive or negative) of rotation, using the word acceleration in its technical kinematical sense." cyon states that the semicircular canals only indirectly assist in giving a notion of spatial relations. "he holds that knowledge of the position of bodies in space depends on nervous impulses coming from the contracting ocular muscles; that the oculomotor centres are in intimate physiological relationship with the centres receiving impulses from the nerves of the semicircular canals; and that the oculomotor centres, thus excited, produce the movements of the eyeballs, which then determine our notions of spatial relations." these views are supported by experiments of lee on dog-fish. when the fish is rotated round different axes there are compensating movements of the eyes and fins. "it was observed that if the fish were rotated in the plane of one of the canals, exactly the same movements of the eyes and fins occurred as were produced by experimental operation and stimulation of the ampulla of that canal." sewall, in 1883, carried out experiments on young sharks and skates with negative results. lee returned to the subject in 1894, and, after numerous experiments on dog-fish, in which the canals or the auditory nerves were divided, obtained evidence that the ampullae contain sense-organs connected with the sense of equilibrium. it has been found by physicians and aurists that disease or injury of the canals, occurring rapidly, produces giddiness, staggering, nystagmus (a peculiar twitching movement of the muscles of the eyeballs), vomiting, noises in the ear and more or less deafness. it is said, however, that if pathological changes come on slowly, so that the canals and vestibule are converted into a solid mass, none of these symptoms may occur. on the whole, the evidence is in favour of the view that from the semicircular canals nervous impulses are transmitted, which, co-ordinated with impulses coming from the visual organs, from the muscles and from the skin, form the bases of these guiding sensations on which the sense of equilibrium depends. these impulses may not reach the level of consciousness, but they call into action co-ordinated mechanisms by which complicated muscular movements are effected. full bibliographical references are given in the article on "the ear" by j.g. mckendrick, in schafer's _textbook of physiology_, vol. ii. p. 1194. (j. g. m.) equinox (from the lat. _aequus_, equal, and _nox_, night), a term used to express either the moment at which, or the point at which, the sun apparently crosses the celestial equator. since the sun moves in the ecliptic, it is in the last-named sense the point of intersection of the ecliptic and the celestial equator. this is the usual meaning of the term in astronomy. there are two such points, opposite each other, at one of which the sun crosses the equator toward the north and at the other toward the south. they are called vernal and autumnal respectively, from the relation of the corresponding times to the seasons of the northern hemisphere. the line of the equinoxes is the imaginary diameter of the celestial sphere which joins them. the vernal equinox is the initial point from which the right ascensions and the longitudes of the heavenly bodies are measured (see astronomy: _spherical_). it is affected by the motions of precession and nutation, of which the former has been known since the time of hipparchus. the actual equinox is defined by first taking the conception of a fictitious point called the mean equinox, which moves at a nearly uniform rate, slow varying, however, from century to century. the true equinox then moves around the mean equinox in a period equal to that of the moon's nodes. these two motions are defined with greater detail in the articles precession of the equinoxes and nutation. _equinoctial gales._--at the time of the equinox it is commonly believed that strong gales may be expected. this popular idea has no foundation in fact, for continued observations have failed to show any unusual prevalence of gales at this season. in one case observations taken for fifty years show that during the five days from the 21st to the 25th of march and september, there were fewer gales and storms than during the preceding and succeeding five days. equites ("horsemen" or "knights," from _equus_, "horse"), in roman history, originally a division of the army, but subsequently a distinct political order, which under the empire resumed its military character. according to the traditional account, romulus instituted a cavalry corps, consisting of three _centuriae_ ("hundreds"), called after the three tribes from which they were taken (ramnes, tities, luceres), divided into ten _turmae_ ("squadrons") of thirty men each. the collective name for the corps was _celeres_ ("the swift," or possibly from [greek: keles], "a riding horse"); livy, however, restricts the term to a special body-guard of romulus. the statements in ancient authorities as to the changes in the number of the equites during the regal period are very confusing; but it is regarded as certain that servius tuillus found six centuries in existence, to which he added twelve, making eighteen in all, a number which remained unchanged throughout the republican period. a proposal by m. porcius cato the elder to supplement the deficiency in the cavalry by the creation of four additional centuries was not adopted. the earlier centuries were called _sex suffragia_ ("the six votes"), and at first consisted exclusively of patricians, while those of servius tullius were entirely or for the most part plebeian. until the reform of the comitia centuriata (probably during the censorship of gaius flaminius in 220 b.c.; see comitia), the equites had voted first, but after that time this privilege was transferred to one century selected by lot from the centuries of the equites and the first class. the equites then voted with the first class, the distinction between the _sex suffragia_ and the other centuries being abolished. although the equites were selected from the wealthiest citizens, service in the cavalry was so expensive that the state gave financial assistance. a sum of money (_aes equestre_) was given to each eques for the purchase of two horses (one for himself and one for his groom), and a further sum for their keep (_aes hordearium_); hence the name _equites equo publico_. in later times, pay was substituted for the _aes hordearium_, three times as much as that of the infantry. if competent, an eques could retain his horse and vote after the expiration of his ten years' service, and (till 129 b.c.) even after entry into the senate. as the demands upon the services of the cavalry increased, it was decided to supplement the regulars by the enrolment of wealthy citizens who kept horses of their own. the origin of these _equites equo privato_ dates back, according to livy (v. 7), to the siege of veii, when a number of young men came forward and offered their services. according to mommsen, although the institution was not intended to be permanent, in later times vacancies in the ranks were filled in this manner, with the result that service in the cavalry, with either a public or a private horse, became obligatory upon all roman citizens possessed of a certain income. these _equites equo privato_ had no vote in the centuries, received pay in place of the _aes equestre_, and did not form a distinct corps. thus, at a comparatively early period, three classes of equites may be distinguished: (a) the patrician equites _equo publico_ of the _sex suffragia_; (b) the plebeian equites in the twelve remaining centuries; (c) the equites _equo privato_, both patrician and plebeian. the equites were originally chosen by the curiae, then in succession by the kings, the consuls, and (after 443 b.c.) by the censors, by whom they were reviewed every five years in the forum. each eques, as his name was called out, passed before the censors, leading his horse. those whose physique and character were satisfactory, and who had taken care of their horses and equipments, were bidden to lead their horse on (_traducere equum_), those who failed to pass the scrutiny were ordered to sell it, in token of their expulsion from the corps. this inspection (_recognitio_) must not be confounded with the full-dress procession (_transvectio_) on the 15th of july from the temple of mars or honos to the capitol, instituted in 304 b.c. by the censor q. fabius maximus rullianus to commemorate the miraculous intervention of castor and pollux at the battle of lake regillus. both inspection and procession were discontinued before the end of the republic, but revived and in a manner combined by augustus. in theory, the twelve plebeian centuries were open to all freeborn youths of the age of seventeen, although in practice preference was given to the members of the older families. other requirements were sound health, high moral character and an honourable calling. at the beginning of the republican period, senators were included in the equestrian centuries. the only definite information as to the amount of fortune necessary refers to later republican and early imperial times, when it is known to have been 400,000 sesterces (about l3500 to l4000). the insignia of the equites were, at first, distinctly military--such as the purple-edged, short military cloak (_trabea_) and decorations for service in the field. with the extension of the roman dominions, the equites lost their military character. prolonged service abroad possessed little attraction for the pick of the roman youth, and recruiting for the cavalry from the equestrian centuries was discontinued. the equites remained at home, or only went out as members of the general's staff, their places being taken by the _equites equo privato_, the cavalry of the allies and the most skilled horsemen of the subject populations. the first gradually disappeared, and roman citizens were rarely found in the ranks of the effective cavalry. in these circumstances there grew up in rome a class of wealthy men, whose sole occupation it was to amass large fortunes by speculation, and who found a most lucrative field of enterprise in state contracts and the farming of the public revenues. these tax-farmers (see publicani) were already in existence at the time of the second punic war; and their numbers and influence increased as the various provinces were added to the roman dominions. the change of the equites into a body of financiers was further materially promoted (a) by the lex claudia (218 b.c.), which prohibited senators from engaging in commercial pursuits, especially if (as seems probable) it included public contracts (cf. flaminius, gaius); (b) by the enactment in the time of gaius gracchus excluding members of the senate from the equestrian centuries. these two measures definitely marked off the aristocracy of birth from the aristocracy of wealth--the landed proprietor from the capitalist. the term equites, originally confined to the purely military equestrian centuries of servius tullius, now came to be applied to all who possessed the property qualification of 400,000 sesterces. as the equites practically monopolized the farming of the taxes, they came to be regarded as identical with the _publicani_, not, as pliny remarks, because any particular rank was necessary to obtain the farming of the taxes, but because such occupation was beyond the reach of all except those who were possessed of considerable means. thus, at the time of the gracchi, these _equites-publicani_ formed a close financial corporation of about 30,000 members, holding an intermediate position between the nobility and the lower classes, keenly alive to their own interests, and ready to stand by one another when attacked. although to some extent looked down upon by the senate as following a dishonourable occupation, they had as a rule sided with the latter, as being at least less hostile to them than the democratic party. to obtain the support of the capitalists, gaius gracchus conceived the plan of creating friction between them and the senate, which he carried out by handing over to them the control (a) of the jury-courts, and (b) of the revenues of asia. (a) hitherto, the list of jurymen for service in the majority of processes, both civil and criminal, had been composed exclusively of senators. the result was that charges of corruption and extortion failed, when brought against members of that order, even in cases where there was little doubt of their guilt. the popular indignation at such scandalous miscarriages of justice rendered a change in the composition of the courts imperative. apparently gracchus at first proposed to create new senators from the equites and to select the jurymen from this mixed body, but this moderate proposal was rejected in favour of one more radical (see w.w. fowler in _classical review_, july 1896). by the lex sempronia (123 b.c.) the list was to be drawn from persons of free birth over thirty years of age, who must possess the equestrian census, and must not be senators. although this measure was bound to set senators and equites at variance, it in no way improved the lot of those chiefly concerned. in fact, it increased the burden of the luckless provincials, whose only appeal lay to a body of men whose interests were identical with those of the _publicani_. provided he left the tax-gatherer alone, the governor might squeeze what he could out of the people, while on the other hand, if he were humanely disposed, it was dangerous for him to remonstrate. (b) the taxes of asia had formerly been paid by the inhabitants themselves in the shape of a fixed sum. gracchus ordered that the taxes, direct and indirect, should be increased, and that the farming of them should be put up to auction at rome. by this arrangement the provincials were ignored, and everything was left in the hands of the capitalists. from this time dates the existence of the equestrian order as an officially recognized political instrument. when the control of the courts passed into the hands of the property equites, all who were summoned to undertake the duties of judices were called equites; the _ordo judicum_ (the official title) and the _ordo equester_ were regarded as identical. it is probable that certain privileges of the equites were due to gracchus; that of wearing the gold ring, hitherto reserved for senators; that of special seats in the theatre, subsequently withdrawn (probably by sulla) and restored by the lex othonis (67 b.c.); the narrow band of purple on the tunic as distinguished from the broad band worn by the senators. various attempts were made by the senate to regain control of the courts, but without success. the lex livia of m. livius drusus (q.v.), passed with that object, but irregularly and by the aid of violence, was annulled by the senate itself. in 82 sulla restored the right of serving as judices to the senate, to which he elevated 300 of the most influential equites, whose support he thus hoped to secure; at the same time he indirectly dealt a blow at the order generally, by abolishing the office of the censor (immediately revived), in whom was vested the right of bestowing the public horse. to this period mommsen assigns the regulation, generally attributed to augustus, that the sons of senators should be knights by right of birth. by the lex aurelia (70 b.c.) the judices were to be chosen in equal numbers from senators, equites and tribuni aerarii (see aerarium), (the last-named being closely connected with the equites), who thus practically commanded a majority. about this time the influence of the equestrian order reached its height, and cicero's great object was to reconcile it with the senate. in this he was successful at the time of the catilinarian conspiracy, in the suppression of which he was materially aided by the equites. but the union did not last long; shortly afterwards the majority ranged themselves on the side of julius caesar, who did away with the tribuni aerarii as judices, and replaced them by equites. augustus undertook the thorough reorganization of the equestrian order on a military basis. the _equites equo privato_ were abolished (according to herzog, not till the reign of tiberius) and the term equites was officially limited to the _equites equo publico_, although all who possessed the property qualification were still considered to belong to the "equestrian order." for the _equites equo publico_ high moral character, good health and the equestrian fortune were necessary. although free birth was considered indispensable, the right of wearing the gold ring (_jus anuli aurei_) was frequently bestowed by the emperor upon freedmen, who thereby became _ingenui_ and eligible as equites. tiberius, however, insisted upon free birth on the father's side to the third generation. extreme youth was no bar; the emperor marcus aurelius had been an eques at the age of six. the sons of senators were eligible by right of birth, and appear to have been known as _equites illustres_. the right of bestowing the _equus publicus_ was vested in the emperor; once given, it was for life, and was only forfeitable through degradation for some offence or the loss of the equestrian fortune. augustus divided the equites into six _turmae_ (regarded by hirschfeld as a continuation of the _sex suffragia_). each was under the command of a _sevir_ ([greek: hilarchos]), who was appointed by the emperor and changed every year. during their term of command the _seviri_ had to exhibit games (_ludi sevirales_). under these officers the equites formed a kind of corporation, which, although not officially recognized, had the right of passing resolutions, chiefly such as embodied acts of homage to the imperial house. it is not known whether the _turmae_ contained a fixed number of equites; there is no doubt that, in assigning the public horse, augustus went far beyond the earlier figure of 1800. thus, dionysius of halicarnassus mentions 5000 equites as taking part in a review at which he himself was present. as before, the equites wore the narrow, purple-striped tunic, and the gold ring, the latter now being considered the distinctive badge of knighthood. the fourteen rows in the theatre were extended by augustus to seats in the circus. the old _recognitio_ was replaced by the _probatio_, conducted by the emperor in his censorial capacity, assisted by an advisory board of specially selected senators. the ceremony was combined with a procession, which, like the earlier _transvectio_, took place on the 15th of july, and at such other times as the emperor pleased. as in earlier times, offenders were punished by expulsion. in order to provide a supply of competent officers, each eques was required to fill certain subordinate posts, called _militiae equestres_. these were (1) the command of an auxiliary cohort; (2) the tribunate of a legion; (3) the command of an auxiliary cavalry squadron, this order being as a rule strictly adhered to. to these septimius severus added the centurionship. nomination to the _militiae equestres_ was in the hands of the emperor. after the completion of their preliminary military service, the equites were eligible for a number of civil posts, chiefly those with which the emperor himself was closely concerned. such were various procuratorships; the prefectures of the corn supply, of the fleet, of the watch, of the praetorian guards; the governorships of recently acquired provinces (egypt, noricum), the others being reserved for senators. at the same time, the abolition of the indirect method of collecting the taxes in the provinces greatly reduced the political influence of the equites. certain religious functions of minor importance were also reserved for them. in the jury courts, the equites, thanks to julius caesar, already formed two-thirds of the judices; augustus, by excluding the senators altogether, virtually gave them the sole control of the tribunals. one of the chief objects of the emperors being to weaken the influence of the senate by the opposition of the equestrian order, the practice was adopted of elevating those equites who had reached a certain stage in their career to the rank of senator by _adlectio_. certain official posts, of which it would have been inadvisable to deprive senators, could thus be bestowed upon the promoted equites. the control of the imperial correspondence and purse was at first in the hands of freedmen and slaves. the emperor claudius tentatively entrusted certain posts connected with these to the equites; in the time of hadrian this became the regular custom. thus a civil career was open to the equites without the obligation of preliminary military service, and the emperor was freed from the pernicious influence of freedmen. after the reign of marcus aurelius (according to mommsen) the equites were divided into: (a) _viri eminentissimi_, the prefects of the praetorian guard; (b) _viri perfectissimi_, the other prefects and the heads of the financial and secretarial departments; (c) _viri egregii_, first mentioned in the reign of antoninus pius, a title by right of the procurators generally. under the empire the power of the equites was at its highest in the time of diocletian; in consequence of the transference of the capital to constantinople, they sank to the position of a mere city guard, under the control of the prefect of the watch. their history may be said to end with the reign of constantine the great. mention may also be made of the _equites singulares augusti_. the body-guard of augustus, consisting of foreign soldiers (chiefly germans and batavians), abolished by galba, was revived from the time of trajan or hadrian under the above title. it was chiefly recruited from the pick of the provincial cavalry, but contained some roman citizens. it formed the imperial "swiss guard," and never left the city except to accompany the emperor. in the time of severus, these equites were divided into two corps, each of which had its separate quarters, and was commanded by a tribune under the orders of the prefect of the praetorian guard. they were subsequently replaced by the _protectores augusti_. see further article rome: _history_; also t. mommsen, _romisches staatsrecht_, iii.; j.n. madvig, _die verfassung des romischen staates_, i.; r. cagnat in daremberg and saglio's _dictionnaire des antiquites_, where full references to ancient authorities are given in the footnotes; a.s. wilkins in smith's _dictionary of greek and roman antiquities_ (3rd ed., 1891); e. belot, _histoire des chevaliers romains_ (1866-1873); h.o. hirschfeld, _untersuchungen auf dem gebiete der romischen verwaltungsgeschichte_ (berlin, 1877); e. herzog, _geschichte und system der romischen staatsverfassung_ (leipzig, 1884-1891); a.h. friedlander, _sittengeschichte roms_, i. (1901); a.h.j. greenidge, _history of rome_, i. (1904); j.b. bury, _the student's roman empire_ (1893); t.m. taylor, _political and constitutional history of rome_ (1899). for a concise summary of different views of the _sex suffragia_ see a. bouche-leclercq's _manuel des antiquites romaines_, quoted in daremberg and saglio; and on the _equites singulares_, t. mommsen in _hermes_, xvi. (1881), p. 458. (j. h. f.) equity (lat. _aequitas_), a term which in its most general sense means equality or justice; in its most technical sense it means a system of law or a body of connected legal principles, which have superseded or supplemented the common law on the ground of their intrinsic superiority. aristotle (_ethics_, bk. v. c. 10) defines equity as a better sort of justice, which corrects legal justice where the latter errs through being expressed in a universal form and not taking account of particular cases. when the law speaks universally, and something happens which is not according to the common course of events, it is right that the law should be modified in its application to that particular case, as the lawgiver himself would have done, if the case had been present to his mind. accordingly the equitable man ([greek: epieikes]) is he who does not push the law to its extreme, but, having legal justice on his side, is disposed to make allowances. equity as thus described would correspond rather to the judicial discretion which modifies the administration of the law than to the antagonistic system which claims to supersede the law. the part played by equity in the development of law is admirably illustrated in the well-known work of sir henry maine on _ancient law_. positive law, at least in progressive societies, is constantly tending to fall behind public opinion, and the expedients adopted for bringing it into harmony therewith are three, viz. legal fictions, equity and statutory legislation. equity here is defined to mean "any body of rules existing by the side of the original civil law, founded on distinct principles, and claiming incidentally to supersede the civil law in virtue of a superior sanctity inherent in those principles." it is thus different from legal fiction, by which a new rule is introduced surreptitiously, and under the pretence that no change has been made in the law, and from statutory legislation, in which the obligatory force of the rule is not supposed to depend upon its intrinsic fitness. the source of roman equity was the fertile theory of natural law, or the law common to all nations. even in the institutes of justinian the distinction is carefully drawn in the laws of a country between those which are peculiar to itself and those which natural reason appoints for all mankind. the connexion in roman law between the ideas of equity, nature, natural law and the law common to all nations, and the influence of the stoical philosophy on their development, are fully discussed in the third chapter of the work we have referred to. the agency by which these principles were introduced was the edicts of the praetor, an annual proclamation setting forth the manner in which the magistrate intended to administer the law during his year of office. each successive praetor adopted the edict of his predecessor, and added new equitable rules of his own, until the further growth of the irregular code was stopped by the praetor salvius julianus in the reign of hadrian. the place of the praetor was occupied in english jurisprudence by the lord high chancellor. the real beginning of english equity is to be found in the custom of handing over to that officer, for adjudication, the complaints which were addressed to the king, praying for remedies beyond the reach of the common law. over and above the authority delegated to the ordinary councils or courts, a reserve of judicial power was believed to reside in the king, which was invoked as of grace by the suitors who could not obtain relief from any inferior tribunal. to the chancellor, as already the head of the judicial system, these petitions were referred, although he was not at first the only officer through whom the prerogative of grace was administered. in the reign of edward iii. the equitable jurisdiction of the court appears to have been established. its constitutional origin was analogous to that of the star chamber and the court of requests. the latter, in fact, was a minor court of equity attached to the lord privy seal as the court of chancery was to the chancellor. the successful assumption of extraordinary or equitable jurisdiction by the chancellor caused similar pretensions to be made by other officers and courts. "not only the court of exchequer, whose functions were in a peculiar manner connected with royal authority, but the counties palatine of chester, lancaster and durham, the court of great session in wales, the universities, the city of london, the cinque ports and other places silently assumed extraordinary jurisdiction similar to that exercised in the court of chancery." even private persons, lords and ladies, affected to establish in their honours courts of equity. english equity has one marked historical peculiarity, viz. that it established itself in a set of independent tribunals which remained in standing contrast to the ordinary courts for many hundred years. in roman law the judge gave the preference to the equitable rule; in english law the equitable rule was enforced by a distinct set of judges. one cause of this separation was the rigid adherence to precedent on the part of the common law courts. another was the jealousy prevailing in england against the principles of the roman law on which english equity to a large extent was founded. when a case of prerogative was referred to the chancellor in the reign of edward iii., he was required to grant such remedy as should be consonant to honesty (_honestas_). and honesty, conscience and equity were said to be the fundamental principles of the court. the early chancellors were ecclesiastics, and under their influence not only moral principles, where these were not regarded by the common law, but also the equitable principles of the roman law were introduced into english jurisprudence. between this point and the time when equity became settled as a portion of the legal system, having fixed principles of its own, various views of its nature seem to have prevailed. for a long time it was thought that precedents could have no place in equity, inasmuch as it professed in each case to do that which was just; and we find this view maintained by common lawyers after it had been abandoned by the professors of equity themselves. g. spence, in his book on the _equitable jurisdiction of the court of chancery_, quotes a case in the reign of charles ii., in which chief justice vaughan said: "i wonder to hear of citing of precedents in matter of equity, for if there be equity in a case, that equity is an universal truth, and there can be no precedent in it; so that in any precedent that can be produced, if it be the same with this case, the reason and equity is the same in itself; and if the precedent be not the same case with this it is not to be cited." but the lord keeper bridgeman answered: "certainly precedents are very necessary and useful to us, for in them we may find the reasons of the equity to guide us, and besides the authority of those who made them is much to be regarded. we shall suppose they did it upon great consideration and weighing of the matter, and it would be very strange and very ill if we should disturb and set aside what has been the course for a long series of times and ages." selden's description is well known: "equity is a roguish thing. 'tis all one as if they should make the standard for measure the chancellor's foot." lord nottingham in 1676 reconciled the ancient theory and the established practice by saying that the conscience which guided the court was not the natural conscience of the man, but the civil and political conscience of the judge. the same tendency of equity to settle into a system of law is seen in the recognition of its limits--in the fact that it did not attempt in all cases to give a remedy when the rule of the common law was contrary to justice. cases of hardship, which the early chancellors would certainly have relieved, were passed over by later judges, simply because no precedent could be found for their interference. the point at which the introduction of new principles of equity finally stopped is fixed by sir henry maine in the chancellorship of lord eldon, who held that the doctrines of the court ought to be as well settled and made as uniform almost as those of the common law. from that time certainly equity, like common law, has professed to take its principles wholly from recorded decisions and statute law. the view (traceable no doubt to the aristotelian definition) that equity mitigates the hardships of the law where the law errs through being framed in universals, is to be found in some of the earlier writings. thus in the _doctor and student_ it is said: "law makers take heed to such things as may often come, and not to every particular case, for they could not though they would; therefore, in some cases it is necessary to leave the words of the law and follow that reason and justice requireth, and to that intent equity is ordained, that is to say, to temper and mitigate the rigour of the law." and lord ellesmere said: "the cause why there is a chancery is for that men's actions are so divers and infinite that it is impossible to make any general law which shall aptly meet with every particular act and not fail in some circumstances." modern equity, it need hardly be said, does not profess to soften the rigour of the law, or to correct the errors into which it falls by reason of its generality. to give any account, even in outline, of the subject matter of equity within the necessary limits of this article would be impossible. it will be sufficient to say here that the classification generally adopted by text-writers is based upon the relations of equity to the common law, of which some explanation is given above. thus equitable jurisdiction is said to be exclusive, concurrent or auxiliary. equity has _exclusive_ jurisdiction where it recognizes rights which are unknown to the common law. the most important example is trusts. equity has _concurrent_ jurisdiction in cases where the law recognized the right but did not give adequate relief, or did not give relief without circuity of action or some similar inconvenience. and equity has _auxiliary_ jurisdiction when the machinery of the courts of law was unable to procure the necessary evidence. "the evils of this double system of judicature," says the report of the judicature commission (1863-1867), "and the confusion and conflict of jurisdiction to which it has led, have been long known and acknowledged." a partial attempt to meet the difficulty was made by several acts of parliament (passed after the reports of commissions appointed in 1850 and 1851), which enabled courts of law and equity both to exercise certain powers formerly peculiar to one or other of them. a more complete remedy was introduced by the judicature act 1873, which consolidated the courts of law and equity, and ordered that law and equity should be administered concurrently according to the rules contained in the 26th section of the act. at the same time many matters of equitable jurisdiction are still left to the chancery division of the high court in the first instance. (see chancery.) authorities.--the principles of equity as set out by the following writers may be consulted: j. story, j.w. smith, h.a. smith and w. ashburner; and for the history see g. spence, _the equitable jurisdiction of the court of chancery_ (2 vols., 1846-1849); d.m. kerly, _historical sketch of the equitable jurisdiction of the court of chancery_ (1890).