126 ANATOMY OF VERTEBRATES. 



deltoid, and shoulder joint ; and is then continued as the ^ musculo- 

 spiral,' supplying the brachialis internus and biceps, and, as it 

 passes behind the antibrachium, the extensors of the pinion; 

 it also distributes filaments to the skin. The next large branch 

 from the plexus is the ' median nerve,' which sends off the ^ ex- 

 ternal cutaneous ' in its course along the biceps, supplying the 

 skin on the outer or radial side of the wing. The ^ ulnar ' nerve 

 is the next branch, supplying the ^ ulnaris internus ; ' and the 

 continuation of the ^median' gives branches to the muscles on 

 the radius, to those on the pinion, and to the integument. 



The nerves of the pelvic limbs are derived from the sacral 

 plexus. The obturator nerve, formed by the second and third sacral 

 nerves, passes through the upper part of the foramen ovale, gives 

 off a branch to join the ' saphenus nerve,' and is distributed to the 

 muscles around the hip-joint. The femoral nerve passes out of 

 the pelvis in company with an artery, over the front edge of the 

 ilium. It divides into three branches, which are dispersed among 

 the muscles, fig. 35, 4o, 42, and integuments on the anterior and 

 inner part of the thigh. One of these filaments represents the 

 ' saphenus,' and descends superficially for a considerable way upon 

 the limb. 



The ischiatic nerve is derived from five or six of the nerves 

 constituting the sacral plexus, on quitting which, even within the 

 pelvis, it is easily separable into its primary branches. Im- 

 mediately after it passes through the ischiatic foramen it sends 

 filaments to the muscles on the outer part of the thigh ; it then 

 proceeds under the biceps, along the back of the thigh, about the 

 middle of which it becomes divided into the tibial and the peroneal 

 nerves. 



The posterior tibial nerve, before it arrives in the ham, sepa- 

 rates into several branches, Avhich pass on each side of the blood- 

 vessels, and are chiefly distributed to the muscles, fig. 35, 46, 50, 

 51, on the back of the leg. Two of these branches, however, 

 are differently disposed of; the one accompanies the posterior 

 tibial artery down the leg, passes over the internal part of the 

 pulley, and is lost in small filaments and anastomoses with a 

 branch of the peroneal nerve on the inner side of the metatarsus ; 

 the other branch runs down on the peroneal side of the leg, along 

 the deep-seated flexors of the toes, ib. 52, passes in a sheath 

 formed for it on the outer edge of the moveable pulley of the heel, 

 and proceeds under the flexor tendons along the metatarsal bone, 

 to be distributed to the internal part of the two external toes. 



The jjeroneal nerve is directed to the outer part of the leg ; it 



