THE LUMBO-SACRAL PLEXUS. 117 



large number and their shortness. Those of the deep layer are supplied by 

 filaments from a single long and thick branch, which descends between the 

 perforatus and the internal gastrocnemius. It may be remarked, that the 

 filament going to the so-called small plantar muscle, passes underneath the 

 external gastrocnemius, outside the perforatus, and that, by its position, it 

 exactly represents the soleus ramuscule of Man. We are. therefore, with 

 Vicq-d'Azyr, Cuvier, and others, justified in naming this little muscle the 

 solearis (soleus), instead of continuing to designate it the small plantaris, 

 which appellation is given to another muscular element. 



6. In its course along the tendo-Achillis, the sciatic nerve emits some 

 slender cutaneous filaments, which we do not consider worthy of further 

 notice. 



TERMINAL BRANCHES. 



PLANTAR NERVES (Fig. 355, 10, 12). These two nerves enter the 

 tarsal sheath, behind the perforans tendon, along with the plantar arteries. 

 Towards the superior extremity of the cannon, they definitively separate 

 from each other; the external is carried outwards between the precited 

 tendon and the rudimentary metatarsal bone ; the internal is placed with 

 that tendon, and follows the posterior border of the inner metatarsal bone. 

 Both afterwards descend on the fetlock, where they comport themselves 

 like the analogous nerves of the anterior limb. 



DIFFERENTIAL CHARACTERS IN THE LUMBO-SACRAL PLEXVS OF OTHER THAN SOLIPED 



ANIMALS. 



As was the case with the brachial plexus, so with this; the differences observed 

 being trifling in the upper part of the limb, but more num. rous and important in the 

 region of the foot, the complr xity of arrangement varying with the species. 



RUMINANTS. The lumbo-sacral plexus of these animals is constituted by two lumbar 

 and three sacral nerves, as in Solipeds; but the third sacral only gives a very fine 

 filament, which reaches the second in passing downward and forward. 



At the femoro-tibial articulation, the branches of the plexus are similar to those in 

 the Horse. Below that articulation, the following disposition has been observed in 

 the Sheep. 



The mufculo-cutaneous branch of the popliteal is long and thick. It descends on the 

 'anterior face of the metatarsus, and at the metatarso-phalangea! aiticub.tion bifurcates, 

 the branches forming the dorsal collaterals of the digits. The anterior tibial nerve 

 presents two branches parallel to the tibial vessels ; one passes along the metatarsal 

 region, and when it arrives at the bottom of the groove between tie condyles of the 

 metatarsus, it divides into two branches that constitute the d< ep collaterals of the 

 diiiits; these colla'erals furnish filaments to the posterior face of the digital region. 



The great sciatic resembles that of Solipeds. Its terminal branches, or plantar 

 nerves, differ from tho^e of the Horse in the absence of the tians>verse anastomosis that 

 unites the two cords in the region of the tendons. 



PIG. The lumbo-sacral plexus of this animal is composed of two lumbar and three 

 sacral nerves : reckoning, of course, as a sacral nerve, the trunk that escapes from 

 between the last lumbar vertebra and the sacrum. The plexus may be divided into 

 two portions, the first furnishing a femoral and an obturator nerve. The internal 

 miphenous branch of the femoral nerve is long and voluminous; at its or gin it is as 

 large as the branch passing to the anterior muscles of the thigh, and it descends on the 

 inner face of the metatarsus, forming the dorsal collateral of the internal digit. 



The great sdatic is voluminous and round The branches it gives 1o the muscles 

 of the pelvis and femur are disposed nearly as in Solipeds and Ruminants; but 

 differences are observed in the external popliteal and the terminal branches. 



The mutculo cutaneous nerve reaches the metatarsal region, where it separates into 

 three branches, which form the dors-d collaterals of the dibits. 



The anterior tibial nerve descends between the two principal metatarsals, and at the 

 mot of the middle digits divides to anastomose with the plantar nerves. Of th. se the 

 external is small, and gives collaterals to the two external digits; the internal, the 



