f, glutmus internus ; b, iliacus internus ; 10, vastus internus ; 33, sciatic nerve ; 23, poplitmus ; 25, 26, tibialis posticus ; 28, 29, 30, 31, flexor longus digiti pedis ; 24, poplitmal nerve ; 38, posterior tibial nerve ; 40, articular ligaments of the knee ankle and pastern joints; 26, insertion of the tendon of the tibialis posticus into 29, that of the flexor longus digiti pedis ; 11, flexor brevis digiti pedis ; 31, insertion of the tendon of the flexor longus into the coffin bone ; 41, internal cartilage of the hoof.
The extensor proprius minimi digiti. — In the horse this muscle is represented by two muscles. One of these, called by Bourgelat the Heral extensor of the foot, and by Lafosse the extensor of the pastern, is inserted by the intervention of a strong tendon into the side of the first phalanx of the solitary toe that forms the foot. The second muscle, placed between the above and the preceding. muscle, furnishes a similar tendon, which, after passing in front of the carpus, becomes united at an acute angle with that of the former, the two co-operating with each other in extending the foot.
In the Ruminantia likewise this muscle is disposed after two different nianners. In the Cervidm or deer tribe, in which the rudimen tary toes are capable of distinct movements, it furnishes two tendons to the two outer toes ; whilst in oxen, goats, sheep, and an telopes its tendon presents a double inser tion— one into the posterior aspect of the outer finger, the other into the tendon of the extensor communis.
The extensor proprius indicis and the two long extensors of the thumb are, in all the ungulate quadrupeds, entirely wanting.
The abductor longus pollicis is present in all the mammalia, even in the Ruminantia and the Solipeds. In the horse its tendon is implanted into the internal surface of the base of the cannon bone, so that it thus becomes an extensor of the foot (l'extenseur obfique du canon of Bourgelat).
The flexor digitorum sublimis pezforatus and the flexor profundus pezforans.— In the horse these muscles arise in common from the in ternal protuberance of the os humeri, and the two are confounded together for a consider able distance, when the two muscles separate to form two distinct tendons ; of these, that belonging to the flexor sublimis runs beneath the annular ligaments of the carpus, to be in serted into the base of the great pastern bone previously dividing to give passage to the tendon of the profundus on its way to be im planted into the last phalanx or coffin bone of the foot.
In the ungulata the small muscles of the hand would evidently be useless, and accortl ingly in the horse all traces of them are lost, their place being supplied by the peculiar structure of the foot, to be described further on.
Posterior Extremity— Muscles of the Pelvis. —The muscles specially belonging to the pel -vis are the quadratus lumborum and the psoas parrus, which in quadrupeds offer precisely the same arrangement as in man.
Muscles inserted into the os femoris —These are similarly disposed in all the Mammifera possessed of a pelvic extremity, the only differ ences observable being in their proportionate sizes. In the Solipeda the analogue of the glutceus maximus is so small, in comparison of the two other glutmi, that it is named by Bourgelat " le petit fessier," and by Stubbs the glutalis externus. In the human subject the comparative large size of this muscle is rendered necessary in consequence of the erect attitude of the body, which it princi pally assists in maintaining; whilst in quadru peds, from the horizontal position of their bodies, it becomes of very secondary import ance. In the horse it is a comparatively slender muscle, deriving its principal origin from the sacral fascia, but also reinforced by a long slender fasciculus, which descends immediately from the upper portion of the ileum. Its insertion is into the third tro chanter and external rough surface at the upper part of the thigh bone, and also by strong tendinous aponeuroses into the fascia lata.
The Glutceus nzedius is the principal muscle in this region ; it arises extensively front the sacro-iliac aponeurosis, and from the ex ternal surface-of the ileum, from which origin it runs downwards and forwards to be im planted into the outer surface of the great trochanter, and is, moreover, prolonged, by means of a strong posterior fasciculus, to wards the lower extremity of the femur. From this latter circumstance, as well as from its preponderating strength, the glutwus medius may be regarded as being, par excellence, the kicking muscle in these quadrupeds which in stinctively have recourse to this mode of de fence as best suited to their orgadzation.