THE AUTONOMIC NERVE SYSTEM 645 



trunks of the spinal nerves. Each ganglion of the vertebral chain gives 

 origin to one or more of these post-ganglionic branches which pass backward 

 and outward and enter the sheath of the corresponding spinal nerve. In 

 the cervical region, however, where the ganglia do not correspond in number 

 with the cervical spinal nerves, the ganglia give off two or more gray rami. 

 Thus in man the superior cervical ganglion sends branches to the first four 

 cervical nerves. The middle and inferior ganglia send a branch to the fifth 

 and sixth and the seventh and eighth cervical nerves respectively. The first 

 thoracic ganglion sends several branches into the trunks of the nerves that 

 enter into the formation of the brachial plexus. The ganglia in the thoracic, 

 lumbar and sacral regions, send at least one gray ramus, in some instances 

 two, into the sheath of the corresponding thoracic, lumbar and sacral nerves. 



The gray rami which thus enter the sheath of the spinal nerve trunks, pass 

 in company with their efferent motor fibers, to the periphery, to be finally 

 distributed to structures in the skin, viz.: non-striated muscles of blood- 

 vessels, non-striated muscles of hair follicles, and epithelium of sweat-glands. 

 The blood-vessels and sweat-glands of the skin of the neck receive their 

 ganglionic nerve-supply from the superior and middle cervical ganglia; those 

 of the skin of the arm, from the inferior cervical and first thoracic ganglia; 

 those for the skin of the trunk, from the thoracic ganglia; those for the skin 

 of the hip and leg, from the lumbar and upper sacral ganglia; those for the 

 skin of the external genital organs, from the lower sacral ganglia. 



2. The rami viscerales. The fibers composing these branches were sup- 

 posed, as the name implies, to pass directly to viscera, though it is apparent 

 from the course they pursue that they communicate, if not with spinal, at 

 least with cranial nerves. 



The superior cervical ganglion gives off from its cephalic extremity two 

 visceral branches, which subsequently divide and subdivide forming the 

 carotid and cavernous plexuses; from these plexuses slender branches follow 

 the course of the more superficial arteries at least, to their terminations, while 

 others pass into the trunks of the trigeminal, abducent, and the superior and 

 deep petrosal branches of the facial nerve, to be distributed to blood-vessels 

 and glands of special regions of the head and face. Still other branches 

 pass down the neck and in their course become associated with correspond- 

 ing branches from the middle and inferior cervical ganglia. Interlacing in 

 an intricate manner they assist in forming the cardiac plexuses. 



The middle cervical ganglion gives off visceral branches, which in asso- 

 ciation with branches from the inferior cervical ganglion, pass to the thyroid 

 gland to be distributed to the walls of the blood-vessels and to the gland cells 

 as well. Stohr, Berkley and others have shown that fine non-medullated 

 nerve filaments terminate on and between the epithelial cells lining the folli- 

 cles, though the supply is not very abundant. 



The inferior cervical ganglion gives off visceral branches which pass down- 

 ward and forward and are ultimately distributed to the heart-muscle. With 

 these fibers there are usually associated, according to the animal considered, 

 visceral fibers which come from the first thoracic or stellate ganglion. These 

 fibers are known as the sympathetic cardiac fibers and have for the physiolo- 

 gist and clinician great interest as they are associated with the activities of 

 the heart. (See pages 311 and 319.) 



The thoracic, lumbar and sacral ganglia also give off visceral branches 



