874 THE NERVES. 



it terminates by two branches. The anterior of these reaches the back of the hand, and gives 

 off three rarauscules there, which are distributed as follows : the first forms the external dorsal 

 coUateriil of the thumb; the second bifurcates, and constitutes the internal dorsal collateral 

 of the thumb and external collateral of the index ; lastly, the third supplies the internal 

 collateral of the index and exturnal of the moiiius. This branch always anastomoses with the 

 dorsal branch of tlie ulnar. The posterior branch — motor — is expended in the muscles on the 

 posterior and external aspect of the forearm. 



5. The median nerve commences by two branches. One arises in common with the musculo- 

 cutaneous or anterior brachial,and corresponds to the anastomosis found around the axillary artery 

 of the Horse; the other is detached from the trunk common to the ulnar and internal cutaneous. 

 The median runs along the bicep.^, passes in front of the elbo^', and licd beneath the annular 

 ligament of the carpus, where it terminates in furnishing: 1. A filament to the short abductor 

 of the thumb. 2. Palmar rainuscuU'S to the thumb, index, and meilius, and external border of 

 the annularis. This disposition of the medius, therefore, much resembles that of the Cat. 



6. The ulnar nerve passes along the inner border of V\c arm and fore.irm, and divides, a 

 little above the inferior extremity of the olecranon, into twj terminal branches —a dorsal and 

 palmar. The first is directed on the back of the hand, aad separates into three metacarpal 

 branches, which, in their course, furnish the dorsal collaterals of the auriciilaris and annuhiris, 

 and internal collateral of the medius ; the otiier parts of the hand are suj)plied by the radial. 

 The second, or palmar branch, is superficial, and detaches the palmar collaterals of the little 

 finger and internal collateral of the annularis, as well as a deep ramuscule that lies across the 

 interosseous muscles, and is a motor nerve. To resume, we see that this distribution of the 

 terminal branches of the brachial plexus of Man much resembles that described in Carnivora, 

 and especially in the Cat. 



Lumbo-sacral Plexus. 



The last two lumbar pairs^ and the three first sacral, in beooming fused 

 together, form the lumbosacral plexus, which corresponds in every respect — hj its 

 constitution, as well as by its mode of distribution — to the plexus of the thoracic 

 Hmb. 



It is usual, in human anatomy, to describe a lumbar and a sacral plexus, each 

 formed by the inferior branches of all the spinal pairs, the names of which they 

 bear. In our opinion, this course has two inconveniences. At first, it apportions 

 into two fasciculi the nerves of the abdominal limb, and, besides in including m 

 the description of these nerves the first lumbar pair and the last sacral, elements 

 are introduced in this description which are altogether foreign to it. It may be 

 remarked, that the four first lumbar pairs, when they anastomose with each other, 

 do so by very slender filaments ; that they only send some subcutaneous filaments 

 to the posterior limb ; that the two last sacral branches — principally for the genito- 

 urinai7 organs and the posterior extremity of the digestive tube — are usually with- 

 out any direct communication with the others ; that the two last lumbar pairs 

 and the three first sacral are alone fused in the same manner as the brachial plexus, 

 and comport themselves like that plexus in the distribution of their branches. 



It is with some reason, then, that we have described, in a special manner, the 

 inferior branches of the four lumbar pairs and the two last sacral, reserving the 

 fasciculus formed by the five intermediate pairs for a special description, under 

 the name of the lumbo-sacral p)lexus. 



Mode of constitution. — In glancing at this plexus, we may perceive that it ia 

 divided into two portions — an interior and posterior, each having a thick trunk 

 in the centre. 



The first of these trunks is formed by the two above-named lumbar pairs, 

 which join each other after a short course, and after receiving an accessory branch 

 from the fourth pair. The second — wider and thinner than the preceding — com- 

 prises the fibres of the three sacral pairs which escape from beneath the subsacral 

 vessels, and unite in a single fasciculus. These two trunks are connected with, 



