DISSECTION OP THB POSTERIOR LIMB. 75 



of the great sciatic. It passes in between the two heads of the gastro- 

 cnemius muscle, follows for a short distance the posterior border of the 

 perforatus, and at the level of the lower border of the popliteus it is 

 continvied under the name of the posterior tibial nerve. The nerve fur- 

 nishes branches to all the muscles at the back of the leg, viz., both 

 heads of the gastrocnemius, the soleus, the perforatus, the popliteus, 

 the perforans, and the flexor accessorius. The branch to the soleus 

 gains its muscles by passing between the popliteus and the outer head 

 of the gastrocnemius. 



The PosTEEiOR Tibial Nerve (Plate 17) continues the internal 

 popliteal. It is at first deeply placed beneath the inner head of the 

 gastrocnemius, where it crosses the perforatus. Becoming more super- 

 ficial by emerging from beneath the first-named muscle, it descends on 

 the inner side of the leg, in front of the tendo Achillis, being covered by 

 the deep fascia of the leg. At the tarsus it bifurcates to form the 

 external and internal plantar nerves. These accompany the perforans 

 tendon through the tarsal sheath, and are continued through the meta- 

 tarsal and digital regions like the corresponding nerves of the fore limb. 

 The only collateral branches of the posterior tibial nerve are slender 

 cutaneovs Jilaments, one of which is shown in Plate 17, descending over 

 the inner side of the hock. 



The External Popliteal Nerve and the External Saphenous Nerve 

 cross the external head of the gastrocnemius on its outer side (Plate 18). 

 The latter nerve has already been described, and the former should be 

 preserved to be followed in the dissection of the front of the leg. 



Directions. — The outer head of the gastrocnemius and the perforatus 

 should now be detached close to their origin, and turned downwards. 

 This will expose the whole of the pophteus, which must be dissected 

 carefully from the posterior ligament of the stifle and from the tibia, in 

 order to follow the popliteal artery. 



The Popliteal Artery (Plate 17) is the direct continuation of the 

 femoral. In veterinary anatomy the arbitrary line of distinction is 

 usually drawn at the point where the vessel passes in between the heads 

 of the gastrocnemius. It passes over the posterior ligament of the 

 stifle, where it is covered by the popliteus ; and at the tibio-fibular arch 

 it bifurcates to form the anterior and posterior tibial arteries. It gives 

 off— (1) articular branches to the stifle, and (2) muscular branches to the 

 superficial muscles at the back of the leg. 



The Postbrior Tibial Artery (Plate 17) is much the smaller of the 

 two terminal branches of the popliteal. In the first part of its course it 

 is deeply placed beneath the popliteus and the deep and accessory flexors. 

 As it descends, it becomes more superficial, and appears at the posterior 

 border of the flexor accessorius, whose tendon it follows in the same 

 position. A little above the hock it forms an S-shaped curve that 



