180 H O K S E [ANATOMY. it is placed. Its duct leaves the inferior anterior angle, j at first descends a little, and runs forward under cover of the rounded inferior border of the mandibular ramus, then curves up along the anterior margin of the masseter muscle, becoming superficial, pierces the buccinator, and enters the mouth by a simple aperture opposite the middle of the crown of the third premolar tooth. It is not quite so thick as a goosequill when distended, and nearly a foot in length. The submaxillary gland is of very similar texture to the last, but much smaller ; it is placed deeper, and lies with its main axis horizontal. It is elongated and slender, and flattened from within outwards. Its posterior end rests against the anterior surface of the transverse process of the atlas, from which it extends forwards and downwards, slightly curved, to beneath the ramus of the jaw. The duct which runs along its upper and internal border passes forwards in the usual course, lying in the inner side of the sublingual gland, to open on the outer surface of a distinct papillte, situated on the floor of the mouth, half an inch from the middle line, and midway between the lower incisor teeth and the attachment of the frsenum linguoe. The sublingual is represented by a mass of glands lying just beneath the mucous membrane of the floor of the mouth on the side of the tongue, causing a distinct ridge, extending from the frsenum backwards, the numerous ducts opening separately along the summit of the ridge. The buccal glands are arranged in two 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 off. The interior is divided by the character of the lining membrane into two very distinct portions, right and left. Over the latter the dense white smooth epithelial lining of the oesophagus is con tinued, terminating abruptly by a raised crenellated border. Over the right part (rather the larger portion) the mucous membrane has a greyish-red colour and a velvety appearance, and contains very numerous peptic glands, which are want ing in the cardiac portion. The cesophageal orifice is very small, and is guarded by a strong crescentic or rather horseshoe-like band of muscular fibres, which is supposed to be the cause of the difficulty of vomiting in the horse. The small intestine is of great length (80 to 90 feet), its mucous membrane being covered with numerous fine villi. The caecum is of conical form, about 2 feet 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 net sacculated, and, being considerably longer than the distance it has to traverse, is thrown into numerous folds. The liver is tolerably symmetrical in its general arrange ment, 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 pos terior border of the organ; of the central l*Hs thus cut off, the right is rather the larger, and has two fissures in its free border subdividing 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. In most works on the anatomy of the horse this has been confounded with the Spigelian lobe of man. There is no gall-bladder, and the biliary duct enters the duodenum about 6 inches 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 duodenum with the bile-duct, and there is often a second small duct which opens separately near to this. 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 very dilatable, being bordered by cartilages upon which several muscles act. Immediately within the opening of the nostril, the respiratory canal sends oft on its upper and outer side a diverticulum or blind pouch (called " false nostril ") of a conical form, and curved, 2 to 3 inches 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, and 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, diverticula from the Eustachian tubes, and lying behind the upper part of the pharynx, the function of which is also not clearly understood. The larynx has the lateral sacculi well developed, though entirely concealed within the alai of the thyroid cartilage. The trachea divides into two bronchi, one for each lung. Nervous System. The brain differs little, except in details of arrangement of convolutions, from that of other ungulates. The cerebral 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 the ducts of the Harderian gland open. Reproductive System, The testes are situated in a dis tinct sessile or slightly peduncnlated scrotum, into which they descend from the sixth to the tenth month after birth. The accessory generative glands are the two vesicular seminales, with the median third vesicle, or uterus mascu- linus, 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 mammae 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.
