INTEGRATION OF ACTIVITIES 



147 



This second neuron may then join the mixed spinal nerve at the same 

 level of the cord, or pass up or down to nerves at other levels, in which 

 it goes out to the organ which it controls. 



The autonomic system is divided functionally into two major regions. 

 One centers in the middle portion of the spinal cord (chest and small 



Fig. 122. — Autonomic nervous system of man, in part, showing double innervation of 

 each organ and the action of each nerve. Organs on the left, iris of eye, rectum, and 

 bladder; on the right, heart, stomach, and small intestine. Small circles are ganglia. 



of back) and may be called the thoracolumbar system. The other has its 

 center partly in the brain, partly in the lower end of the spinal cord, and is 

 called the craniosacral system (Fig. 122). The chain of neurons described 

 above belongs to the thoracolumbar. The ganglia of the craniosacral 

 system lie in general much farther from the spinal cord, sometimes 

 actually in the organ that is controlled. 



