614 TEXT-BOOK OF PHYSIOLOGY. 



the lateral portion of the gray matter of the spinal cord from the level 

 of the first thoracic nerve to the level of the third or fourth lumbar 

 nerves; 2. in the gray matter beneath the aqueduct of Sylvius just where it 

 enlarges to form the cavity of the third ventricle and in the gray matter beneath 

 the floor of the fourth ventricle; and 3. in the gray matter of the spinal cord 

 at the levels of origin of the second, third, and fourth sacral nerves. The 

 nerve-fibers which thus associate the spinal cord with the ganglia are termed 

 pre-ganglionic fibers in contradistinction to those fibers associating the 

 ganglia with the tissues and organs which are termed post-ganglionic fibers. 



1. The pre-ganglionic fibers that have their origin in nerve-cells in the lateral 



portion of the gray matter of the spinal cord emerge from the cord in 

 the ventral roots of the spinal nerves from and including the first 

 thoracic to the third lumbar nerves. In association with the large 

 efferent fibers composing these roots, the fine medullated fibers pass 

 outward to the point at which the spinal nerve, formed by the union of 

 the ventral and dorsal roots, separates into an anterior and a posterior 

 division. At this point the fine medullated fibers leave the spinal nerve, 

 and after a short course enter the ganglia of the vertebral chain where 

 some of the fibers terminate in ganglia at the same and different levels 

 while others pass forward to terminate in the ganglia of the pre-vertebral 

 chain. On entering the ganglia the peripheral branches of the fibers 

 arborize around the nerve-cells composing them. The short nerve- 

 strands that pass from the spinal nerves to the ganglia are termed 

 from their color white rami communicantes . 



In accordance with their distribution, as determined by histologic 

 and physiologic methods of investigation, these pre-ganglionic fibers 

 may be divided into seven groups, viz. : i. those passing up the vertebral 

 chain to the superior cervical ganglion; 2. those passing to the inferior 

 cervical ganglion; 3. those passing to the first thoracic ganglion; 

 4. those passing directly to the thoracic and upper lumbar ganglia; 5. 

 those passing down the vertebral chain to the lower lumbar and sacral 

 ganglia; 6. those which pass through the thoracic portion of the verte- 

 bral chain and forward to the ganglia of the pre-vertebral chain, 

 (the semilunar, renal, and superior mesenteric) which in their course 

 are known as the splanchnic nerves; 7. those passing through the 

 lumbar portion of the vertebral chain and forward to the inferior 

 mesenteric ganglion in which for the most part they terminate. These 

 nerves are sometimes termed the inferior splanchnics. 



2. The pre-ganglionic fibers that arise from nerve-cells in the gray matter 



beneath the aqueduct of Sylvius enter the trunk of the third or oculo- 

 motor nerve, pass forward in it, as far as the interior of the orbit cavity, 

 where they leave the nerve and terminate around the cells composing 

 the ciliary ganglion. (See page 580.) 



The pre-ganglionic fibers that arise from nerve-cells in the gray matter 

 beneath the floor of the fourth ventricle, leave by three routes, viz., in 

 the trunks of the pars intermedia or nerve of Wrisberg, the glosso- 

 pharyngeal, and the vagus. 



The fibers that leave in the pars intermedia enter the facial nerve 

 and subsequently pass by way of the great superficial petrosal nerve to 



