rows parallel with the molar teeth. The upper ones are the largest,
and are continuous anteriorly with the labial glands, the ducts of
which open on the mucous membrane of the upper lip.
The stomach of the horse is simple in its external form, with a largely developed right cul de sac, and is a good deal curved on itself, so that the cardiac and pyloric orifices are brought near together. The antrum pyloricum is small and not very distinctly marked. The interior is divided by the character of the lining membrane into two distinct portions, right and left. Over the latter the dense white smooth epithelial lining of the œsophagus is continued, terminating abruptly by a raised crenulated border. Over the right part the mucous membrane has a greyish-red colour and a velvety appearance, and contains numerous peptic glands, which are wanting in the cardiac portion. The œsophageal orifice is small, and guarded by a strong crescentic or horseshoe-like band of muscular fibres, supposed to be the cause of the difficulty of vomiting in the horse. The small intestine is of great length (80 to 90 ft.), its mucous membrane being covered with numerous fine villi. The caecum is of conical form, about 2 ft. long and nearly a foot in diameter; its walls are sacculated, especially near the base, having four longitudinal muscular bands; and its capacity is about twice that of the stomach. It lies with its base near the lower part of the abdomen, and its apex directed towards the thorax. The colon is about one-third the length of the small intestine, and very capacious in the greater part of its course. As usual it may be divided into an ascending, transverse, and descending portion; but the middle or transverse portion is folded into a great loop, which descends as low as the pubis; so that the colon forms altogether four folds, generally parallel to the long axis of the body. The descending colon is much narrower than the rest, and not sacculated, and, being considerably longer than the distance it has to traverse, is thrown into numerous folds.
The liver is tolerably symmetrical in general arrangement, being divided nearly equally into segments by a well-marked umbilical fissure. Each segment is again divided by lateral fissures, which do not extend quite to the posterior border of the organ; of the central lobes thus cut off, the right is rather the larger, and has two fissures in its free border dividing it into lobules. The extent of these varies, however, in different individuals. The two lateral lobes are subtriangular in form. The Spigelian lobe is represented by a flat surface between the postal fissure and the posterior border, not distinctly marked off from the left lateral by a fissure of the ductus venosus, as this vessel is buried deep in the hepatic substance, but the caudate lobe is distinct and tongue-shaped, its free apex reaching nearly to the border of the right lateral lobe. There is no gall-bladder, and the biliary duct enters the duodenum about 6 in. from the pylorus. The pancreas has two lobes or branches, a long one passing to the left and reaching the spleen, and a shorter right lobe. The principal duct enters the duedenum with the bile-duct, and there is often a second small duct opening separately.
Circulatory and Respiratory Organs.—The heart has the form of a rather elongated and pointed cone. There is one anterior vena cava, formed by the union of the two jugular and two axillary veins. The aorta gives off a large branch (the anterior aorta) very near its origin, from which arise—first, the left axillary, and afterwards the right axillary and the two carotid arteries.
Under ordinary circumstances the horse breathes entirely by the nasal passages, the communication between the larynx and the mouth being closed by the velum palati. The nostrils are placed laterally, near the termination of the muzzle, and are large and dilatable, being bordered by cartilages upon which several muscles act. Immediately within the opening of the nostril, the respiratory canal sends off on its upper and outer side a blind pouch (“false nostril”) of conical form, and curved, 2 to 3 in. in depth, lying in the notch formed between the nasal and premaxillary bones. It is lined by mucous membrane continuous with that of the nasal passage; its use is not apparent. It is longer in the ass than in the horse. Here may be mentioned the guttural pouches, large air-sacs from the Eustachian tubes, and lying behind the upper part of the pharynx, the function of which is also not understood. The larynx has the lateral sacculi well developed, though entirely concealed within the alae of the thyroid cartilage. The trachea divides into two bronchi.
Nervous System.—The brain differs little, except in details of arrangement of convolutions, from that of other ungulates. The hemispheres are rather elongated and subcylindrical, the olfactory lobes are large and project freely in front of the hemispheres, and the greater part of the cerebellum is uncovered. The eye is provided with a nictitating membrane or third eyelid, at the base of which open the ducts of the Harderian gland.
Reproductive System.—The testes are situated in a distinct sessile or slightly pedunculated scrotum, into which they descend from the sixth to the tenth month after birth. The accessory generative glands are the two vesiculae seminales, with the median third vesicle, or uterus masculinus, lying between them, the single bilobed prostate, and a pair of globular Cowper’s glands. The penis is very large, cylindrical, with a truncated, expanded, flattened termination. When in a state of repose it is retracted, by a muscle arising from the sacrum, within the prepuce, a cutaneous fold attached below the symphysis pubis.
The uterus is bicornuate. The vagina is often partially divided by a membraneous septum or hymen. The teats are two, inguinally placed. The surface of the chorion is covered evenly with minute villi, constituting a diffuse non-deciduate placenta. The period of gestation is eleven months.
Authorities.—R. I. Pocock, “The Species and Subspecies of Zebras,” Ann. Mag. Nat. Hist. ser. 6, vol. xx., 1897, and “A New Arrangement of the Existing Species of Equidae,” Op. cit. ser. 7, vol. x., 1902; R. Lydekker, “Notes on the specimens of Wild Asses in English Collections,” Novitates Zoologicae, vol. xi., 1904; B. Salensky, “On Equus przewalskii,” Mém. Acad. St Pétersburg, 1902; M. S. Arloing, “Organisation du pied chez le cheval,” Ann. Sci. Nat., 1867, viii. 55-81; H. Burmeister, Los caballos fosiles de la Pampa Argentina (Buenos Aires, 1875); Chauveau and Arloing, Traité d’anatomie comparée des animaux domestiques (Paris, 1871), and English edition by G. Fleming (1873); A. Ecker, “Das Europäische Wildpferd und dessen Beziehungen zum domesticirten Pferd,” Globus, Bd. xxxiv. (Brunswick, 1878); Major Forsyth, “Beiträge zur Geschichte der fossilen Pferde besonders Italiens,” Abh. Schw. Pal. Ges. iv. 1-16, pt. iv.; George, “Études zool. sur les Hémiones et quelques autres espèces chevalines,” Ann. Sci. Nat., 1869, xii. 5; E. F. Gurlt, Anatomische Abbildungen der Haussäugethiere (1824), and Hand. der vergleich. Anat. der Haussäugethiere (2 vols., 1822); Huet, “Croisement des diverses espèces du genre cheval,” Nouv. Archives du Muséum, 2nd ser., tom. ii. p. 46, 1879; Leisering, Atlas der Anatomie des Pferdes (Leipzig, 1861); O. C. Marsh, “Notice of New Equine Mammals from the Tertiary Formation,” Am. Journ. of Science and Arts, vol. vii., March 1874; Id., “Fossil Horses in America,” Amer. Naturalist, vol. viii., May 1874; Id., “Polydactyle Horses,” Am. Journ. Sci. and Arts, vol. xvii., June 1879; Franz Müller, Lehrbuch der Anatomie des Pferdes (Vienna, 1853); R. Owen, “Equine Remains in Cavern of Bruniquel,” Phil. Trans. vol. clix., 1870, p. 535; W. Percivall, The Anatomy of the Horse (1832); G. Stubbs, Anatomy of the Horse (1766); W. H. Flower, The Horse (London, 1891); Ridgeway, Origin of the Thoroughbred Horse (1905). (W. H. F.; R. L.*)
History
From the evidence of philology it appears that the horse was already known to the Aryans before the period of their dispersion.[1]
The first mention of the British horse occurs in the well-known passages in Caesar (B.G. iv. 24. 33, v. 15. 16; cf. Pomp. Mela iii. 6), in which he mentions the native “essedarii” and the skill with which they handled their war chariots. We are left quite in the dark as to the character of the animal thus employed; but there would appear to be much probability in the surmise of W. Youatt, who conjectures the horse to have been, “then as ever, the creature of the country in which he lived. With short
- ↑ Compare Sans, açva, Zendish and Old Persian açpa, Lithuanian aszva (mare), Prussian asvinan (mare’s milk), O.H. Ger. ehu, A.S. eoh, Icel. iör, Gothic aihos, aihous (?), Old Irish ech, Old Cambrian and Gaelic ep (as in Epona, the horse goddess), Lat. equus, Gr. ἵππος or ἴκκος. The word seems, however, to have disappeared from the Slavonic languages. The root is probably ak, with the idea of sharpness or swiftness (ἄκρος, ὠκύς, acus, ocior). See Pott, Etym. Forsch, ii. 256, and Hehn, Kulturpflanzen u. Hausthiere in ihrem Uebergang aus Asien nach Griechenland u. Italien sowie in das übrige Europa (3rd ed., 1877), p. 38. The last-named author, who points out the absence of the horse from the Egyptian monuments prior to the beginning of the 18th century B.C., and the fact that the earliest references to this animal in Hebrew literature (Judges v. 22, 28; cf. Josh, xi. 4) do not carry us any farther back, is of opinion that the Semitic peoples as a whole were indebted for the horse to the lands of Iran. He also shows that literature affords no trace of the horse as indigenous to Arabia prior to about the beginning of the 5th century A.D., although references abound in the pre-Islamitic poetry. Horses were not numerous even in Mahomet’s time (Sprenger, Leb. Moh. iii. 139, 140). Compare Ignazio Guidi’s paper “Della sede primitiva dei popoli Semitici” in the Transactions of the Accademia dei Lincei (1878–1879), Professor W. Ridgeway, in his Origin and Influence of the Thoroughbred Horse (1905), reinvestigated the historical mystery as to the Arab breed, and its connexion with the English thoroughbred stock, but his conclusions have been hotly controverted; archaeology and biology are in fact still in the dark on the subject, but see the section on “Species” above. According to Ridgeway, the original source of the finest equine blood is Africa, still the home of the largest variety of wild Equidae; he concludes that thence it passed into Europe at an early time, to be blended with that of the indigenous Celtic species, and thence into western Asia into the veins of an indigenous Mongolian species, still represented by “Przewalski’s horse”; not till a comparatively late period did it reach Arabia, though the “Arab” now represents the purest form of the Libyan blood. The controversy depends upon the consideration of a wealth of detail, which should be studied in Ridgeway’s book; but zoological authorities are sceptical as to the suggested species, Equus caballus libycus.
