LUMBO-SACRAL PLEXUS. 511 



The Metacarpal nerves, external and internal, are formed, 

 the fir^t by the union of a branch from the median and one from 

 the cubital ; the second may be regarded as the continuation of 

 the median. They run down the metacarpus by the sides of the 

 flexor tendons, to which they give filaments, and terminate at- 

 the fetlock ; the internal nerve lies posterior to the great meta- 

 carpal artery. Midway down the metacarpus, they anastomose 

 by means of an oblique branch which crosses the flexor tendons 

 posteriorly. At the fetlock, near the insertion of the suspensory^ 

 ligament to the sesamoids, each metacarpal nerve divides into- 

 three digital branches ; anterior, middle, and posterior. 



The anterior branch descends in front of the digital vein, and 

 distributes its branches on the anterior surface of the foot. The 

 middle branch frequently anastomoses with the others, and always 

 with the anterior branch. It supplies the fetlock pad and sensi- 

 tive sole. The posterior branch, by far the largest, and the true 

 continuation of the metacarpal nerve, is continued behind the 

 digital artery to the basilar process of the os pedis, entering the 

 lateral fissure, and being distributed to the substance of the bone 

 and the laminae. It gives off branches to the flexor tendons, 

 and a filament which is carried forwards and distributed to the 

 sensitive frog ; minute filaments accompany the plantar ungual 

 artery into the pedal bone. 



LUMBO-SACRAL PLEXUS. 

 (Fig. 192;) 



This plexus, which supplies the posterior extremity, is formed 

 by the inferior branches of the last two lumbar and the first three 

 sacral nerves; it is divided into two portions, an anterior or 

 lumbar, and a posterior sacral, each of which has a large trunk 

 for its centre. The anterior division is constituted by the above- 

 mentioned lumbar nerves, receiving, after a short course, a branch 

 from the fourth one ; the posterior division is formed by the first 

 three sacral nerves, which unite to form a single bundle. These 

 trunks are united by communicating branches. 



The anterior division is buried under the psoas parvus, and 

 is separated from the posterior division by the internal iliac artery. 

 The posterior division is placed within and on the side of the 

 pelvic cavity. The anterior division furnishes the iliaco-mus- 

 cular, crural, and obturator nerves. The posterior division gives 



