GROSS ANATOMICAL RELATIONS 665 



below the region of the first dorsal, but there are only three cervical ganglia 

 in the neck and certain ganglia of questionable horn ology in the head region. 

 This chain of ganglia is known in the historical anatomical literature and 

 in the older physiological literature as the sympathetic system. 



There are, however, numerous other outlying ganglia such as the gan- 

 glia of the celiac axis, the superior mesenteric and hypogastric plexuses, as 

 well as such secondary or collateral plexuses as the aortic, renal, etc. 

 From these ganglia nerves are distributed to other parts of the system and 

 to the motor end mechanisms. The small ganglia in connection with 

 those branches of the fifth and other cerebral nerves which are distributed 

 in the neighborhood of the organs of special sense, namely, the ophthalmic, 

 otic, spheno- palatine, and submaxillary ganglia, etc., all belong to the cranial 

 autonomies as we shall presently see. Similar small ganglia are found on 

 the sacral autonomic pathways. 



Physiologically there are two functional types of nerve fibers, afferent 

 and efferent, which run in autonomic pathways. The former or afferent 

 fibers arise in the sensory epithelium of the alimentary canal, lungs or 

 blood vessels, and from special sense organs such as the pacinian corpuscles 

 of the mesentery. The second or efferent group constitutes the autonomic 

 system proper. It is to this group that the cells of the sympathetic ganglia 

 of all kinds belong. 



There is still a third order of nerve-cell collections or ganglia found in 

 the walls of hollow organs. The chief and best known of these ganglionic 

 networks are found in the walls of the stomach and intestinal canal and are 

 known as the plexuses of Auerbach, and of Meissner. Smaller collections 

 of this type are found in the walls of the urinary bladder, the ureter, the 

 uterus and vagina, and in different divisions of the male genital system. 

 The term enteric system is applied to this type of nerve structure, specific- 

 ally that part typical of the alimentary canal. These nets, which are for 

 the most part microscopic, are also freely connected with other parts of 

 the system, as well as with the cerebro-spinal axis. 



Gross Anatomical Relations. No special interest attaches to the gross 

 anatomical relations outside of the fact that these factors are guides to the 

 complicated neurone relations in which our present interest in the autono- 

 mic system lies. The ganglia of the sympathetic chain typically corre- 

 spond segment by segment with the spinal nerves with which they are 

 connected. The type arrangement is shown in figure 417. Each ganglion 

 is connected with its corresponding spinal nerve by two nerve branches, 

 the white and gray rami. 



The secret of the presence of the two kinds of rami is revealed by the 

 work of Gaskell on the type and character of the constituent neurones of 

 the white and gray rami and of the spinal nerves, and of Langley and 

 Anderson on the neurone connections and neurone pathways. It has been 



