874 TEE NERVES. 



it terminates by two brauches. The anterior of these reaches the back of the liand, and gives 

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

 collateriil 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 external of the medius. This brancli always anastomoses with the 

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

 posterior and external aspect of the forearm. 



5. Thti 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; tiie other is detached from the trunk common to the ulnar and internal cutaneous. 

 The median runs along the biceps, passes in front of the elbow, and lies beneath the annular 

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

 of the thumb. 2. Palmar ramuscules to the thumb, index, and medius, 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 the arm and forearm, and divides, a 

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

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

 branches, which, in their course, furnish the dorsal collaterals of the auricularis and annularis, 

 and internal collateral of the medius ; the otiier parts of the hand are supplied 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 lu Carnivora, 

 and especially in the Cat. 



Lumbo-sacral Plexus. 



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

 together, form the lumbo-sacral plexus, which corresponds in every respect — by its 

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

 limb. 



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 in 

 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- 

 urinary 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 plexus. 



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

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

 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 smgle fasciculus. These two trunks are connected with 



