PNEUMOGASTRIC NERVES. 



91 



Fig. 33. Relation of Spinal Cord and 

 Sympathetic Nervous System (Diagram). 



ganglia in the body cavity, one along each side of the spinal 

 column, receiving branches from the spinal nerves, and sending 

 branches to all the internal organs of the body, the heart and 

 lungs in the thorax, and the 



Stomach, intestines, and the Sympathetic Nerve Chains 



other organs of the abdominal 

 cavity. In many places these 

 nerves form a thick 

 network called a 

 plexus. One very 

 large plexus is on 

 the posterior sur- 

 face of the stomach, and is 

 called the Solar Plexus. 



The Pneumogastric Nerves 

 are a pair of the cranial nerves 

 arising from the sides of the 

 spinal bulb ; and, passing downward, they give branches to the 



pharynx, gullet, and stom- 

 ach, the larynx, windpipe, 

 and lungs, and the 

 heart. Now, what- 

 ever O ther function 

 the pneumogastric 

 nerves may have, they 

 seem to have the power of 

 retarding, or stopping al- 

 together, the beat of the 

 heart ; and stimulation of 

 the pneumogastric nerves may make the heart pause in a re- 

 laxed condition. Other nerves may quicken the heart-beat, 

 but the pneumogastrics are regarded as a brake on the heart's 

 action. 



Spinal Cord 



Sympathetic 

 Ganglion 



Fig. 34. Ideal Cross Section of the 



Nervous System. (After Lan- 



dois & Stirling.) 



