550 H. W. NORRIS AND SALLY P. HUGHES 



the first rib and thence, in the interval between the dorsal and 

 subvertebral trunk muscles, to the vicinity of the sympathetic 

 trunk {sp.2v.). On the way it divides into a) a motor branch 

 soon entering the rectus subvertebralis muscle and running 

 through it as far as the series of sections continues (sp. 2vmsv.), 

 gradually diminishing in size as it gives off fibers to the muscle; 

 h) a sensory branch, containing a few motor fibers {sp.2vc.). 

 This latter branch passes through the second sympathetic 

 ganglion, leaving the motor fibers within the ganglion, and, on 

 emerging, runs laterally and ventrally to unite with the first 

 spinal nerve as noted in the preceding section. Farther anteri- 

 orly from this union the sensory cutaneous fibers (second spinal 

 nerve) separate from the motor fibers (first spinal nerve) and 

 are distributed laterally and ventrally to the skin of the posterior 

 head and anterior trunk regions. The small group of motor 

 fibers, introduced into the sympathetic ganglion along with the 

 cutaneous branch of the second spinal nerve, divides within the 

 ganglion. The two minute branches thus formed pass out at 

 the extreme posterior end of the ganglion, one of them uniting 

 with a small branch of the third spinal nerve. With a small 

 group of fibers of the latter it forms a small nerve that fuses with 

 the other branch which arose from the division within the ganglion. 

 The resulting nerve (fig. 44, sp.2 + 3vm.) passes posteriorly to 

 innervate the muscle described by Wiedersheim as the 'serratus.' 



THE THIRD SPINAL NERVE 



The third spinal nerve conforms very closely to the plan of 

 the second. A dorsal and a lateral ramus have a composition 

 and a distribution similar to the corresponding branches of the 

 second spinal nerve. The ventral ramus divides into : a) a motor 

 branch which runs some distance at the lateral border of the 

 rectus subvertebralis musculature, then enters the latter to con- 

 tinue a course similar to the corresponding branch of the second 

 spinal; h) a cutaneous division which, like the corresponding 

 branch of the second spinal, contains motor fibers. This cu- 

 taneous nerve passes out posterolaterally through the ventral 



