172 ANATOMY OF VERTEBRATES. 



of the ulnar, having a similar destination on the outer side of the 

 foot. The musculo-spiral nerve arises from the seventh cervical and 

 first and second dorsal nerves : after supplying the heads of the 

 triceps, it passes round the humerus, and gives branches to the 

 two large extensors at the back of the fore-leg, and sends a 

 branch, somewhat expanded, down to the carpal joints, but not 

 swelling into a ganglion, as in Man ; it then pierces the rudiment 

 of the short supinator, to supply a muscle answering to the long 

 supinator on the outer side of the back of the fore-arm. 



In the Pig, the median in the fore-arm is much larger than the 

 ulnar; it receives a small communicating branch from the ulnar 

 near the wrist, and then supplies the inner small toe (it), both 

 sides of the inner large toe (Hi), and the inner side of the next 

 (iv). The ulnar gives off the dorsal branch, and then sends 

 the deep palmar to the interosseous muscles ; it contributes a small 

 branch to the median, and then supplies the outer side of the 

 large toe (iv), and the adjoining small toe (v). The greatest 

 portion of the dorsum of the foot is furnished by the radial branch 

 of the spiral nerve, and the rest by the dorsal branch of the ulnar. 



In the Ass there are eighteen pairs of dorsal nerves, the 

 anterior or ventral divisions of which pass between the ribs, are 

 distributed to the intercostal and abdominal muscles, the hind- 

 most perforating the psoas muscle. There are five lumbar 

 and six sacral nerves, besides four or five caudal. The third 

 lumbar sends off a branch, which gives a branch to the great 

 psoas muscle, and one to join the fourth for the anterior crural 

 nerve ; it then becomes the external cutaneous nerve to pass on 

 the outer side of the thigh ; it sends off another large branch 

 corresponding with the external spermatic, which communicates 

 with a large branch of the third lumbar ganglion of the sympa- 

 thetic, gives a branch to the small psoas muscle, and then 

 passes underneath the lower border of the abdominal muscles, to 

 which it sends a branch, and becomes distributed on the mamma. 

 The anterior crural nerve arises from the third, fourth, and 

 fifth lumbar nerves : the obturator arises from the fourth and 

 fifth lumbar, and first sacral nerves : the sciatic arises from 

 the three first sacrals : the principal part of the third and 

 fourth sacrals, joined by a small branch from the portion of the 

 sciatic arising from the second, give off the internal pudendal to 

 pass at the side of the arch of the pubes, distribute filaments 

 to the neck of the bladder, and terminate on the clitoris, vagina, 

 and external parts, and the connecting muscle and membrane 

 between these and the mamma. A branch of the external sper- 



