290 



THE BIOLOGY OF THE FROG 



CHAP. 



br.ftl 



aci.pl 



Sj.A 



which are distributed to the 

 fore limb and muscles of the 

 shoulder. 



The third pair of nerves, 

 after giving a branch to the 

 brachial plexus, supplies the 

 anterior part of the external 

 oblique and transversus mus- 

 cles and gives some twigs to 

 the skin. 



The fourth, fifth, and 

 sixth nerves are small and 

 are distributed mainly to the 

 skin and muscles of the wall 

 of the abdomen. 



The seventh, eighth, and 

 ninth nerves pass almost 

 directly backward and anas- 

 tomose with each other to 

 form the lumbosacral, or 

 sciatic plexus. The seventh 

 nerve, before it enters the 

 plexus, gives off the ileo- 

 hypogastric nerve, which is 



distributed to the muscles 

 of the abdomen. The cru- 

 ralis nerve is given off from 



I-X, spinal nerves ; Ao, 



FIG. 82. — Spinal nerves and sympa- 

 thetic system of the frog, the right 

 side seen from below. Only the 

 ventral branches of the spinal 

 nerves shown. Sympathetic system in black, 

 systemic arch of aorta; br.pl, brachial plexus; C, calcareous bodies, 

 around the spinal ganglia; D.Ao, dorsal aorta; fern, femoral nerve; 

 II. A, iliac artery; sc, sciatic nerve; sci.pl, sciatic plexus; Sk, skull; 

 Sp.A, splanchnic, or cceliaco-mesenteric artery; Sy, sympathetic cord; 

 Sy.c, commissures between sympathetic and spinal nerves ; Sy.g, 

 sympathetic ganglia; Ust, urostyle; V l -V$, centra of vertebrae; Vg t 

 vagus nerve. (From Parker and Parker.) 



