THE LUMBO-SAURAL PLEXUS. 879 



and membranosus, and the great adductor of the thigh. Arriving towards the 

 superior extremity of the leg, it enters between the two bellies of the gastroc- 

 nemius muscle, passes along the posterior aspect of the perforatus muscle, and 

 descends in the channel of the hock, beneath the tibial aponeurosis, following 

 the internal border of the fibrous band that reinforces the tendon of the hock. 

 It finally terminates at the calcis by two branches — the external and internal 

 plantar nerves. 



From the point at which the great sciatic enters between the bellies of the 

 gastrocnemius muscle, and as far as the furrow of the calcis, this nerve corre- 

 sponds to the branch named in Man the " internal popliteal " — a branch that is 

 continued by the posterior tibial, which terminates in the plantar filaments. 



In its long course, this nerve successively gives off : 1. The external popliteal 

 nerve, 2. A branch to the muscles of the deep pelvi-crural region. 3. Another 

 to the posterior crural muscles. 4. The external saphenous nerve. 5. A 

 voluminous fasciculus to the muscles of the posterior tibial region. All these 

 branches will be studied, more especially the external popliteal — which is so 

 disposed in Solipeds, that Veterinary authorities have described it as a special 

 trunk, by the name of the " small femoro-popliteal," and even as the " small 

 sciatic nerve." We will afterwards pass to the terminal branch. 



Collateral Branches of the Great Sciatic Nerve. 



1. EXTEENAL POPLITEAL OR SmALL FeMORO-POPLITEAL NeRVE. — This 



nerve separates from the great sciatic at the gemelli muscles of the pelvis. It 

 is then directed forward and downward, proceeds between the biceps and the 

 gastrocnemius muscles, and arrives outside the superior extremity of the leg, 

 behind the lateral ligament of the femoro-tibial articulation, where it terminates 

 by two branches — the musculo-mtaneous, and the anterior tibial nerve. 



In the long course it follows from its origin to its bifurcation, the external 

 pophteal nerve only furnishes a single collateral branch — this is the cutaneous 

 nerve which is detached from the parent trunk above the gastrocnemius, and 

 traverses the inferior extremity of the biceps to terminate by divergent ramuscules 

 to the skin of the leg. It might be named the peroneal-cutaneous branch. Before 

 becoming superficial, this cutaneous nerve gives off a small descending filament 

 which goes to reinforce the external saphenous nerve, after creeping over the 

 aponeurotic layer of the external portion of the gastrocnemius. This branch — 

 which might be designated the accessory of the external saphenous — sometimes 

 proceeds directly from the popliteal, as may be remarked in Fig. 475. 



Terminal Branches. — These two branches stimulate the muscles belonging to 

 the anterior tibial region, and endow the skin on the anterior surface of the foot 

 with sensation. 



The musculo-cutaneous nerve is situated beneath the tibial aponeurosis ; it 

 first sends a bundle of ramuscules to the lateral extensor of the phalanges, and 

 continues to descend between that muscle and its congener — the anterior extensor 

 — to the middle of the tibia. It then traverses the fibrous envelope of the tibial 

 muscle, becomes subcutaneous, and gains the anterior face of the metatarsus, 

 where it is lost in the skin. Some of its terminal filaments may be followed to 

 the fetlock, and even beyond it (Fig. 475, 6). 



The anterior tibial nerve passes in front of the preceding, to one side of the 

 superior extremity of the leg, and then plunges beneath the anterior extensor of 



