According to some authors, it represents the peroneus tertius; but that muscle is situated on the outer side of the common extensor of the toes; and here the portion with which it has been compared is placed on the inside. It has also been likened to a portion of the common extensor of the toes, but it does not pass to the latter. Lastly, it has been considered as being the homologue of the proper extensor of the great-toe; but why, then, in the ox, which has no great-toe, is it so highly developed? Nevertheless, its position and its relations sufficiently warrant this method of comprehending it. The tibialis anticus is a flexor of the foot. It is also able, in animals in which the tarsal articulations allow of the movement, to rotate the foot inwards. [Illustration: 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_.