THE NERVOUS SYSTEM 375 



of vegetative life. The main trunks of this system are two in number, one 

 running on either side of the vertebral column, extending from tlie head 

 backward as far as the tail. 



Each in its course has upon it a number of small round or ovoid 

 bodies termed ganglia. These consist of a covering of connective tissue, 

 from which small septa pass into the interior. The spaces thus formed 

 in the organs are filled in with small cells, some of which are round, 

 while others have proceeding from them small fibres or poles, by which 



Fig. 



-Diagram of the Ganglia of the Sympathetic System of Nerves 



' Superior Cervical Ganglion. -, - Cervical Sympathetic Cord. ^ Middle Cervical Ganglion, •* Inferior Cervical 

 Ganglion. ^ Cervical Poi'tion of Sympathetic. ^, ^ Dorsal Sympathetic. ^ Lumbar Portion of Sympathetic. 

 8 Sacral Portion of Sympathetic. ^ Great Splanchnic Nerve. " Lesser Splanchnic Nerve. i' Solar Ganglion. 

 ^- Afferent Branches from Spinal Pairs. " Pelvic Plexus. '* Branch to Pelvic Plexus. '^ Spermatic Plexus. 

 16 Posterior Mesenteric Plexus. ^^ Branches from Posterior to Anterior Mesenteric Plexus. ^^ Lurnbo-Aortic 



Plexus. li' Superior (Esophageal Branch. "> Inferior CEsophageal Branch. -• Cardiac Nerves. " Branch to 

 Pelvic Plexus. ^3 Conjoined Cord of Pneumogastric and Sympathetic Nei-ves. 



they are connected with nerve -tubes, which go to (afferent) and come 

 from the ganglia (efferent). Some nerve -fibres also pass through the 

 ganglia, and in doing so are brought into contact with the cells. 



As the sympathetic chain runs along the side of the vertebrae, a small 

 ganglion appears upon it, opposite to each intervertebral gap or hole, out 

 of which the spinal nerves emerge. 



The spinal nerves on passing out of the .spinal canal divide into an 

 upper and a lower branch, and from each of the latter a few fibres proceed 

 to the sympathetic ganglia and reinforce the sympathetic chain. 



The different parts of the sympathetic cord are distinguished by terms 

 indicating the region with which they are connected, hence the terms 

 cervical or neck, the dorsal or back, the lumbar or loin, and the sacral or 

 croup plexuses or nerves. 



