74 THE ANATOMY OF THE HOBSB. 



nislies 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 ilexor accessorius. The branch to the soleus gains 

 its muscle by passing between the popliteus and the outer head of the 

 gastrocnemius. 



The PosTBEioH 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 

 asternal 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 

 cutaneous filaments, one of which is shown in Plate 1 7, descending over 

 the inner side of the hook. 



The External Popliteal Nbevb and the External Saphenous NsRvi) 

 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 popliteus, 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 h^anches to 

 the superficial muscles at the back of the leg. 



The Posterior 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 acoessoiy 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 posi- 

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

 into company with the terminal part of the posterior tibial nerve ; and 

 passing with that nerve into the tarsal sheath, it divides at the back of 

 the hock into the two plantar arteries. The collateral branches of the 

 posterior tibial are — (1) muscular branches to the deep muscles at the 



