THE LUMSO-SACRAL PLEXUS. 775 



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 ter- 

 minal branches. 



COLLATERAL BllANCHES. 



1. EXTERNAL SCIATIC-POPLITEAL, OR SMALL FEMORO-POPLITEAL NERVE. 

 This nerve separates from the great sciatic at the gemini muscles of the 

 pelvis. It is then directed forward and downward, proceeds between the 

 triceps cruris 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- cutaneous, and 

 the anterior tibial nerve. 



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

 sciatic popliteal nerve only furnishes a single collateral branch : this is the 

 cutaneous nerve which is detached from the parent trunk above the gastro- 

 cnemius, and which traverses the inferior extremity of the triceps cruris, to 

 terminate by divergent ramuscles destined 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 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. 35-7. 



Terminal Branches. These two branches influence the contractility of 

 the muscles belonging to the anterior tibial region, and endow the skin on 

 the anterior face 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. 357, 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 ex- 

 tensor of the phalanges, giving to that muscle and the flexor of the metatarsus 

 short, but thick, ramuscules. It descends to the front of the tarsus, always 

 covered by the anterior extensor of the phalanges, and placed at the external 

 side of the anterior tibial vessels. When it arrives below the tibia, it lies 

 immediately alongside the pedal artery, and follows it, in its metatarsal 

 portion, to near the fetlock. It then separates from its satellite vessel, and 

 passes on the side of the digit, where it ends by the emission of cutaneous 

 filaments (Fig. 357, 5). 



Among the ramuscules this nerve abandons in its course, are cited those 

 which carry nervous influence to the pedal muscle. 



2. BRANCHES TO THE MUSCLES OP THE DEEP PELVI-CRURAL EEGION. 

 It is known that this region comprises the obturator internus, gemini, and 

 quadratus femoris muscles. The nervous branch sent to them is long and 

 attenuated ; it is detached from the sciatic trunk at the middle of the super- 

 cotyloid ridge, and descends with that trunk behind the coxo-femoral 

 articulation, to distribute its terminal divisions to the above-named muscles. 



