714 PHYSIOLOGY. 



As to the bulbar origin, the autonomic efferent fibers of the 

 vagus end in the cardiac ganglia, from which postganglionic fibers 

 run to the cardiac muscle. In its course the vagus meets small 

 groups of nerve-cells in the lungs, the external wall of the oeso- 

 phagus, and the stomach. 



The vagus sends many fibers to the (enteric nervous system) 

 Meissner-Auerbach ganglia in the stomach, furnishing secretory 

 nerves to the stomach and pancreas; and the number of its fibers 

 in its downward course to the intestine diminish, and are completely 

 absent in the descending colon. The bulbar autonomic system 

 innervates the upper part of the digestive tract, from the mouth to 



Fig. 289. Diagram of the Main Distribution of the Bulbar and Sacral 

 Autonomic Fibers. (LANGLEY.) 



The bulbar fibers supply the anterior end of alimentary canal and the sali- 

 vary glands. The sacral fibers supply the posterior end of the alimentary canal 

 and the external generative organs. The sympathetic supplies the whole tract 

 and also the skin and the internal generative organs which receive no involun- 

 tary fibers from any other source. 



the descending colon, and the cavities and organs in connection, as 

 the salivary glands, the lungs, the liver, and the pancreas. The 

 sacral ?,utonomic nerves innervate the lower part of the digestive 

 tract, the descending colon, anus, bladder, and, by their nervi 

 erigentes, the external genitals. The sphincter of the iris and 

 ciliary muscle receives no fibers from the spinal thoracic sympathetic, 

 but only cranial autonomic nerves. The bulbar and sacral autonomic 

 systems are independent of the spinal thoracic sympathetic system 

 as regards development, and are not a part of the spinal sympathetic 

 system. 



A long series of fibers arise from the thoracic and upper lumbar 

 spinal cord. These are the fibers of the sympathetic nervous system, 



