354 



THE MAINTENANCE OF THE INDIVIDUAL 



following braticlios : (] ) a dorsal branch; (2) a nioro prominent ventral 

 branch, whicli supplies the skin and body nuisculaturc ; (,S) a com- 

 municating branch, going to 

 the ganglia of the autonomic 

 system and thence to the 

 viscera ; and (4) a small 

 meningeal branch, going back 

 to the protective layers of 

 the cord. Thus the nerves 

 emanating from this point of 

 fusion are mixed in character 

 while their roots are not. 



mesonterii 

 ganglion 



cfcrsol raot 



ganglion^ 



dorsal root 

 Ventral root 



rocmrcs 

 Communi- 



\ir.. 



; visntroli? 



Components of a spinal nerve. Somatic 

 motor fibers are indicated by solid lines; 

 \ isceral motor by lonp dashes; somatic sen- 

 sory in short dashes ; \ isceral sensory by 

 dotted lines. 



The Autonomic Nervous 

 System 



The term autonomic nervous 

 system embraces all nerves 

 and ganglia located outside of 

 the spinal cord, which reg- 

 ulate the activities of smooth, 

 or involuntary, muscle and 

 various glands. It should 

 also be thought of as an auxiliary, or perhaps more properly a relay 

 apparatus to supplement the work of the central nervous system. 



Anatomically the system consists of two ''longitudinally con- 

 nected" chains of ganglia lying on either side and just ventral to the 

 cerebrospinal cord together with various ganglia scattered throughout 

 the viscera and groups of connecting nerves extending to the central 

 nervous system. This system is divisible into two parts. The first 

 is called the thoracicolumbar jiart, and consists of the double chain of 

 ganglia mentioned above together with the connections through the 

 spinal nerves. It reaches the blood vessels, heart, digestive tract, and 

 many other parts of the body. The second, or parasympathetic part, 

 is characterized by having three centers, two cranial centers, one in 

 the mid-brain, one in the medulla region, and a posterior center in the 

 sacral region. 



Masses of nervous tissue are scattered as ganglia which are located 

 in various organs, such as the walls of the digestive tract, where they 

 are known as the solar, cardiac, or aortic plexvses. These serve as relay 

 centers for impulses coming from the main trimk line of the autonomic 



