THE LUMBOSACRAL PLEXUS. 881 



way, it occupies the same situation outside the hock that the great sciatic does 

 on the inner side. It afterwards passes over the tarsal region, and is expended 

 on the outside of the metatarsus in several filaments, some of which descend 

 to the outer aspect of the digit (Figs. 473, 11, 12 ; 475, 9). 



5. Fasciculi to the Posterior Tibial Muscles.— This fasciculus is 

 composed of numerous branches, which are detached together from the sciatic 

 nerve on its passage between the two portions of the gastrocnemius muscle, in 

 the form of a thick short trunk. The muscles of the superficial layer — the 

 gastrocnemius, perforatus, and the thin fleshy band, improperly designated the 

 " small plantaris " by Veterinarians — receive ramuscules which are remarkable for 

 their large number and their shortn 'ss. Those of the deep layer are supplied 

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

 perforatus and the internal portion of the gastrocnemius. It may be remarked, 

 that the filament going to the so-called small plantaris muscle passes underneath 

 the external division of the gastrocnemius, outside the perforatus, and that, by 

 its position, it exactly represents the soleus ramuscule in Man. We are, therefore 

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

 soleus, instead of continuing to designate it the small plantaris, which appellation 

 is given to another muscle. 



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. 473, 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-sackal Plexus of the other Animals. 



As was tlie case with the brachial plexus, so with this; the diflferences observed being 

 trifling in the upper part of the limb, but more numeious and important in the region of the 

 foot, the complexity ot arrangement varying with the species. 



Ruminants. — The lumbo-sacral plexus of these animals is constituted by two lumbar and 

 tl\ree sacral nerves, as in Solipeds ; but tlie 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. 



Tlie muscido-cutaneous branch of the popliteal is long and thick. It descends on the 

 anterior face of the metatarsus, and at the metatnrso-phalangeal articulation 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 the condyles of the metatarsus, it divides into two 

 branches that constitute the deep collaterals of the digits ; these collaterals 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 those of the Horse, in the absence of the transverse 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 



