SYMPATHETIC NERVOUS SYSTEM. 255 



do not return as postganglionic fibers by the gray ramus to the 

 same spinal nerve. On the contrary, the gray ramus of the twelfth 

 thoracic may consist of the postganglionic portion of autonomic 

 fibers that enter the sympathetic through a white ramus of 

 one of the higher thoracic nerves. In general, we may say 

 that there is a great outflow of autonomic fibers, including 

 vasomotor, sweat, and pilomotor fibers, in the white rami commu- 

 nicantes from the first or second thoracic to the second or fourth 

 lumbar nerves. Those of these fibers that are to be distributed to 

 the skin areas of the body head, limbs, and trunk return by way 

 of the gray rami to the various spinal nerves and are distributed with 

 these nerves, the distribution being somewhat different in different 

 animals and for the several varieties of fibers. Those fibers that 

 are distributed eventually to the blood-vessels, glands, and walls 

 of the viscera have a different course from those supplying the 

 glands, blood-vessels, and plain muscle of the head region. For 

 the head region the fibers after entering the sympathetic chain pass 

 upward along the cervical sympathetic to end in the superior 

 cervical ganglion; thence the path is continued by postganglionic 

 fibers which emerge by the various plexuses that arise from this 

 ganglion. For the abdominal and pelvic viscera the fibers (particu- 

 larly the rich supply of vasoconstrictor fibers), after entering the 

 sympathetic chain, emerge, still as preganglionic fibers, by the 

 splanchnic nerves that run to the celiac ganglia or in the branches 

 connecting with the inferior mesenteric ganglia, and then become' 

 postganglionic fibers (see Fig. 112). The details of the course of 

 the vasomotor, sweat, visceromotor fibers to the different regions, 

 the cardiac fibers, etc., will be given in the appropriate sections. 



General Course of the Autonomic Fibers Arising from the 

 Brain Tectal and Bulbar Autonomies. These fibers leave 

 the brain in the third, seventh, ninth, tenth, and eleventh cranial 

 nerves. Those that emerge in the third nerve end, as preganglionic 

 fibers, in the ciliary ganglion. Their postganglionic fibers leave 

 this ganglion in the short ciliary nerves and innervate the plain 

 muscle of the sphincter of the iris and the ciliary muscle. The 

 fibers that emerge in the seventh and ninth nerves probably supply 

 the glands and blood-vessels (vasodilator fibers) of the mucous 

 membrane of the nose and mouth. Some of these fibers reach the 

 fifth nerve by way of anastomosing branches and are distributed 

 with it. Their preganglionic portion terminates in some of the 

 ganglia belonging to the sympathetic type which are found in this 

 region, such as the sphenopalatine and otic ganglia, and the sub- 

 maxillary and sublingual ganglia for the fibers distributed to the 

 glands of the same name. The autonomic fibers that arise with 

 the tenth (and the eleventh) nerves are distributed through the 



