In the horse, its fleshy body is but slightly developed, so that its tendon alone is specially visible in the superficial muscular layer, but in the dog and the cat it is large. Hence it results that its fleshy body appears on each side of the inferior half of the gastrocnemius, and produces an elevation which recalls that which the soleus produces on each side of the same muscles in the human species. The muscles which follow form, with the popliteus, which we have already studied, the deep layer of the posterior region of the leg. =Flexor Longus Digitorum= (Fig. 87, 19; Fig. 88, 17).--This muscle, in man, is the only common flexor of the toes belonging to the muscles of the leg. In comparison with the preceding muscle, it is a deep flexor. Veterinarians have given it the name of _the oblique flexor of the phalanges_. Visible on the internal aspect of the superficial layer of the muscles of the leg, this muscle arises above from the posterior surface of the external tuberosity of the tibia, becomes tendinous, passes towards the metatarsus, and blends with the tendons of the posterior tibial and the long proper flexor of the great-toe. In the dog and the cat it is blended with this latter only. =Tibialis Posticus= (Fig. 85, 14; Fig. 86, 12; Fig. 87, 20; Fig. 88, 16).--This muscle arises from the external tuberosity of the tibia, and from the head of the fibula. Thence it passes to the tarsus, and terminates in different fashion in carnivora and other quadrupeds. In the dog and the cat, it is inserted into the ligamentous apparatus of the tarsus, or into the base of the second metatarsal. In the other quadrupeds with which we are here occupied it is blended with the long proper flexor of the great-toe. It is accordingly in the carnivora that the mode of termination of the tibialis posticus most nearly resembles that of this same muscle in the human species. From this independence there results a special action. It is an adductor and internal rotator of the foot. =Flexor Longus Pollicis= (Fig. 84, 18; Fig. 85, 14; Fig. 86, 12; Fig. 87, 18; Fig. 88, 16).--This muscle, as that in man, is the most external of the deep layer of the leg. It is on the external aspect of the latter we perceive it, between the peroneals and the gastrocnemius or tendo-Achillis. It arises from the fibula and tibia, and is thence directed towards the tarsus. It unites with the long common flexor of the toes to form with it _the deep flexor of the phalanges_, of which it is the principal fasciculus. We may add that in the dog and the cat the posterior tibial remains independent of this latter, but that in the pig, ox, and horse the posterior tibial is united to the preceding to form with them the deep flexor muscle.