632 THE AUTONOMIC NERVOUS SYSTEM 



must leave the cerebrospinal channels and enter the sympathetic 

 ganglia. This transfer is accomplished in three different regions, 

 namely, by way of the: 



A. Cranial nerves. 



(a) Midbrain, third nerve and gangl. ciliare. 



(6) Bulb. (1) Second branch of the trigeminus, gangl. sphenopalatinum. (2) 

 Third branch of the trigeminus and gangl. oticum et gangl. submaxillare. 

 (3) Vagus and glossopharyngeus. 



B. Thoracic and lumbar divisions of the spinal cord, from the first thoracic to the 

 fourth lumbar nerves. 



C. Sacral division of the spinal cord, over the nerv. pelvicus. 



We have previously seen that the sympathetic system as originally 

 described, consists of a chain of ganglia and their connections situated 

 along the vertebral column in the region of the thoracic and lumbar 

 segments of the spinal cord. But the autonomic system also includes 

 a number of ganglia and plexuses which do not belong to this particu- 

 lar region of the nervous system, but form the anatomically distinct 

 parasympathetic system. The latter embraces the cranial and sacral 

 ganglia. To summarize, the autonomic nervous system consists of 

 the sympathetic and parasympathetic systems. The latter includes 

 all those ganglia and plexuses which are not directly related to the 

 thoracic and lumbar divisions of the spinal cord. A glance at Fig. 311 

 will show that the largest number of the viscera receive a double 

 nerve supply, namely, one from the sympathetic system proper and 

 one from the parasympathetic system. 1 Peculiarly enough, the func- 

 tions of these two groups of fibers are generally antagonistic to one 

 another. In illustration of this statement might be mentioned the 

 variations in the size of the pupil, or in the action of the heart. In 

 the former case, the stimulation of the oculomotor nerve representing 

 the autonomic pathway from the midbrain, gives pupillar constriction 

 and the excitation of the cervical sympathetic, pupillar dilatation. 

 In the case of the heart, the bulbar autonomic fibers contained in 

 the vagus nerve, are cardio-inhibitory in their function, and the sym- 

 pathetic, cardio-acceleratory. 



Having found that the cerebrospinal and autonomic systems 

 are connected by definite bridges of fibers, let us for a moment examine 

 the structural details of one of these. I select for this purpose the 

 spinosympathetic rami, because their course has been made out with 

 at least a fair degree of accuracy (Fig. 313). We have seen that the 

 axons of the cells in the anterior horn seek their corresponding motor 

 end-organs by way of the anterior roots (I). In tracing these fibers 

 outward to the point where they intermingle with the afferent fibers 

 tending toward the posterior root, it is noted that a number of them 

 leave the mixed nerve and pursue a straight course toward the sympa- 

 thetic ganglion at the side of the vertebral column (II and III). 



1 Gottlieb and Meyer, Die exper. Pharmak. als Grundlage der Arzeneibehand- 

 lung, Berlin, 1912. 



