Fig. 85.—Myology of the Ox: Left Leg, External Aspect.
1, Gluteus maximus and biceps cruris; 2, semi-tendinosus; 3, patella; 4, tibialis anticus (flexor of the metatarsus); 5, extensor longus digitorum (anterior extensor of the phalanges); 6, fasciculus of the extensor longus digitorum, which is considered as the representative of the tendinous portion of the tibialis anticus in the horse; 7, peroneus longus; 8, peroneus brevis (proper extensor of the external toe); 9, external head of gastrocnemius; 10, soleus; 11, tendo-Achillis; 12, calcaneum; 13, tendon of the extensor longus digitorum (superficial flexor of the phalanges); 14, flexor longus pollicis and tibialis posticus (deep flexor of the phalanges); 15, tendon of the superficial flexor of the toes; 16, tendon of the deep flexor of the toes; 17, suspensory ligament of the fetlock.
With regard to the tendinous part, called by veterinarians the cord of the flexor of the metatarsus, it serves, in the horse, to produce the flexion of the metatarsus when the knee is already flexed; it thus acts in a passive fashion, which is explained by its resistance and the position which it occupies in relation to these two articulations.
Extensor Proprius Pollicis.—This muscle exists only in the dog and the cat, and there in a rudimentary condition.
It is covered by the common extensor of the toes and the tibialis anticus, and passes, accompanied by the tendon of this latter muscle, to terminate on the second metatarsal, or the phalanx, which articulates with it. When the first toe exists in the dog, it is inserted into this by a very slender tendon.
Extensor Longus Digitorum ([Fig. 83], 9; [Fig. 84], 7; [Fig. 85], 5, 6; [Fig. 86], 4; [Fig. 87], 12; [Fig. 88], 7).—It is also called by veterinarians the anterior extensor of the phalanges.
In the dog and the cat this muscle is to be seen in the space limited behind by the peroneus longus and in front by the tibialis anticus. Above it is covered by this latter. In the lower half of the leg, it is also in relation, on the inner side, with the tibialis anticus; but behind it is separated from the peroneus longus by the external surface of the shaft and inferior extremity of the tibia. This arrangement, besides, recalls that which is found in man, the peroneus longus of the latter diverging in the same way, at this level, from the common extensor, and leaving exposed the corresponding portion of the skeleton of the leg.