COMPARATIVE ANATOMY OF THE MUSCULAR SYSTEM 155 



n) Semitendinosus. The most posterior muscle of the thigh, posterior to the 

 preceding. Origin, ischial tuberosity ; insertion, tibia; action, flexor of the shank. 



o) Tenuissimus. Turn to the lateral surface of the thigh. Cut through 

 the middle of the biceps femoris. Beneath it will be noted a very narrow long 

 muscle, the tenuissimus. Origin, transverse process of the second caudal verte- 

 brae, in common with the caudofemoralis; insertion, on the same fascia as the 

 insertion of the biceps. 



On separating the biceps from the underlying muscles they will be revealed 

 as extensions of muscles already identified on the medial surface. The adductor 

 femoris is seen in contact with the femur posterior to the vastus lateralis; the 

 semimembranosus comes next, and the semitendinosus is again the most caudal 

 of the thigh muscles. 



10. The muscles of the shank. 

 Rabbit: 



a) Tibialis anterior. The lateral (outer, dorsal) surface of the shank is 

 covered by the distal end of the biceps femoris and fascia. These should be 

 removed. The most anterior of the muscles of the lateral surface is the tibialis 

 anterior. Origin, lateral condyle and tuberosity of the tibia; insertion, second 

 metatarsal; action, flexor of the foot. 



b) Peroneus. Next dorsal to the preceding on the lateral surface, consisting 

 of a group of several more or less fused muscles. Origin, tibia and fibula; inser- 

 tion, metatarsals; action, flexor of the foot. 



c) Gastrocnemius. This is the thin but broad muscle forming the caudal 

 surface of the shank, divisible into two nearly separate portions, one of which is 

 on the lateral, one on the medial surface of the shank. Origin, lateral and medial 

 condyles of the femur and tibia; insertion, by a strong tendon, the tendon of 

 Achilles, which passes over the heel (calcaneus) on which it is inserted; action, 

 extensor of the foot. 



d) Soleus. This is the muscle just internal to that part of the gastrocnemius 

 which is on the lateral surface of the thigh. Origin, head of the fibula ; insertion 

 and action with the preceding. 



e) Plantaris. This is situated internal to that part of the gastrocnemius 

 which is medial. Origin, lateral condyle of the femur; insertion and action 

 with the preceding. 



/) Other muscles of the shank (optional). There are three more muscles of the 

 shank; they lie in contact with the tibia. They are: the extensor hallucis longus 

 exposed on the medial surface of the tibia; extensor digitorum longus, covered by 

 the tibialis anterior; said flexor digitorum longus, between the tibia and the soleus 

 and plantaris. As their names imply, these muscles are inserted by long 

 slender tendons on the digits and act to flex and extend the digits. 



It should be noted that the muscles named extensor in the shank and foot 

 are really flexor in their action and those named flexor are extensor in their 



