94 DISSECTION OF THE DOG 



The cutaneous nerves of the back of the leg are derived from 

 the saphenous, peroneal, and tibial nerves. The saphenous nerve supplies 

 the medial aspect of the leg and pes. The lateral cutaneous of the calf 

 (n. cutaneus surae lateralis) has been previously noted as arising either from 

 the sciatic or from the peroneal nerve. It becomes superficial at the border 

 of the biceps and supplies the skin of the posterior and lateral parts of the leg. 



N. cutaneus surje medialis. — The medial cutaneous nerve of the calf 

 is a branch of the tibial nerve, and arises a little distance before this nerve 

 sinks between the two heads of the gastrocnemius muscle. Crossing the 

 surface of the gastrocnemius slightly obliquely, along with a branch 

 from the posterior femoral artery and the small saphenous vein, the nerve 

 divides into two branches about the middle of the leg. These immediately 

 pierce the deep fascia and become superficial. The posterior (plantar) branch 

 runs along the lateral side of the tendo-calcaneus [Achillis] and snpplies the 

 skin about the tarsus. The anterior (dorsal) branch runs obliquely between 

 the tendo-calcaneus and the deep flexor of the digits, is connected with the 

 tibial nerve, and ends in the skin of the distal part of the leg, the tarsus and 

 the metatarsus. 



A. saphena. — The origin of the saphenous artery from the femoral was 

 noted in the dissection of the thigh. Crossing the surface of the gracilis and 

 semitendinosus muscles subcutaneously, it arrives in the leg and immediately 

 divides into anterior (dorsal) and posterior (plantar) branches. The anterior 

 branch passes down the leg in association with the large saphenous vein and 

 has been examined in connection with the dorsum of the pes. 



The posterior branch, much the larger, descends upon the deep flexors of 

 the digit in a special compartment of the deep fascia which also contains the 

 corresponding vein and the tibial nerve. A little proximal to the tarsus it 

 supplies the lateral tarsal artery (a. tarsea lateralis) and is continued into the 

 pes, where it will be followed subsequently. 



M. gastrocnemius. — This powerful muscle arises by two heads. The 

 lateral head takes origin from the lateral sesamoid and from the lateral border 

 of the planum poplitaeum of the femur. The medial head arises from the 

 medial sesamoid and the medial border of the planum pophtseum. 



The two heads soon join, and the common muscle thus formed gives place 

 to a strong tendon about the middle of the leg. The insertion is into the 

 tuber of the calcaneus. 



Dissection. — Cut across the gastrocnemius muscle just where its two heads 

 are about to join. The process of reflecting the lateral head is made a 

 little difficult by its close connection with the underlying plantaris muscle. 



M. plantaris. — The plantaris muscle arises in common with the lateral 

 head of the gastrocnemius from the lateral sesamoid bone and the lateral lip 

 of the planum poplitseum. In the distal third of the leg the fleshy belly of the 



