THE SYMPATHETIC SYSTEM 187 



the interior of the skull in company with the internal carotid 

 artery. The most important of these join the semilunar 

 (Gasserian) ganglion and are carried by the naso-ciliary branch 

 of the ophthalmic nerve (p. 66) to the ciliary ganglion, from 

 which they pass forwards to the eyeball to supply the dilator 

 muscle of the pupil. Paralysis of this muscle is an important 

 sign in affections of the sympathetic (p. 189). 



The middle and inferior cervical ganglia give off grey rami 

 communicantes, which join the fifth and sixth and the seventh 

 and eighth cervical nerves, respectively. In this way, the 

 blood-vessels and sweat glands of the upper limb are brought 

 under the control of the sympathetic system. 



In addition, each cervical ganglion gives off a cardiac branch 

 and these branches constitute the accelerator nerves of the heart 

 (p. 308). 



The sympathetic trunk enters the thorax by crossing the 

 anterior aspect of the neck of the first rib and then descends 

 in front of the heads of the ribs. It posseses eleven or twelve 

 thoracic ganglia, and each of these is connected to the inter- 

 costal nerve to which it corresponds by both a white and a 

 grey ramus communicans. As already stated, the white rami 

 contain efferent fibres from the spinal medulla to the sym- 

 pathetic system, and they occur throughout the thoracic region, 

 with the occasional exception of the first thoracic segment. 

 These efferents from the spinal medulla have to supply a 

 very large area, since there are no white rami communicantes 

 in the cervical or in the lower lumbar region. They ascend 

 through the cervical part of the sympathetic trunk, through 

 which they are distributed to the head and neck and upper 

 limb. 



Other sympathetic efferents arise from the thoracic ganglia 

 and pass to be distributed to the contents of the abdomen. 

 They form the splanchnic nerves and the largest of them 

 receives branches from the fifth to the tenth thoracic ganglia, 

 inclusive. The smaller splanchnic nerve arises from the 

 tenth and eleventh and the smallest from the eleventh ganglion. 



