156 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



action, following a custom borrowed from human anatomy. The custom arises 

 from a desire to retain the names applied to the muscles of the fore limb for the 

 muscles in the corresponding positions in the hind limb. Thus in the supine 

 position of the forearm, the extensors face anteriorly and the flexors posteriorly. 

 Similarly the muscles on the anterior side of the leg are designated extensors, 

 although they really flex the foot, and those on the posterior side, flexors, although 

 they extend the foot. In describing the action, the terms flexor and extensor 

 are used with reference to the movement produced and not with reference to 

 the position of the muscle on the limb. 

 Cat: 



a) Tibialis anterior. Clean away the tough fascia of the shank and also 

 the insertions of the biceps and the gracilis. Examine the lateral (outer) surface 

 of the shank. The most ventral muscle whose ventral border is in contact with 

 the tibia is the tibialis anterior. Origin, proximal parts of tibia and fibula; 

 insertion by a strong tendon which should be traced into the foot where it will 

 be found to pass obliquely to the medial side of the foot to be inserted on the 

 first metatarsal; action, flexor of the foot. 



b) Extensor digitorum longus. This is the muscle next dorsal to the preceding 

 on the lateral surface of the shank. It is so closely placed to the preceding as to 

 appear as part of it, but the line of separation will be found by a little searching. 

 Origin, lateral epicondyle of the femur; insertion, by a stout tendon which if 

 followed into the foot is found to diverge into four tendons, one of which is 

 inserted on each digit; action, extensors of the digits. 



c) Peroneus muscles. These are next dorsal to the preceding, originating 

 on the fibula. There are three of them more or less fused to each other. The 

 three end each in a tendon; the three tendons pass over the lateral surface of 

 the lateral malleolus of the tibia and over the calcaneus, and are inserted on 

 the metatarsals and digits. Action, extensors and flexors of the foot. 



d) Gastrocnemius. This is the large muscle forming the posterior or caudal 

 surface of the shank. It is divisible into two large portions, one on the medial 

 surface, the other on the lateral surface of the shank. The lateral head is sub- 

 divisible into four heads. Origins, from the surface fascia, the femur, and the 

 tendon and fascia of the plantaris muscle (see below); insertion, by a strong 

 tendon, which passes to the heel bone (calcaneus) on which it is inserted. Action, 

 extensor of the foot. 



e) Soleus. On carefully separating the lateral head of the gastrocnemius, 

 a muscle, the soleus. will be found internal to it. It is a flat muscle in contact with 

 the peroneus muscles ventrally; it tapers abruptly to a tendon which joins the 

 tendon of the gastrocnemius. Origin, fibula; insertion, calcaneus; action, with 

 the gastrocnemius, of which it is sometimes considered a part. 



/) Plantaris. On carefully separating the medial head of the gastrocnemius 

 a large muscle will be found internal to it, lying between the two heads of the 

 gastrocnemius which practically inclose it. It is fused to a considerable extent 



