THE CRANIAL NERVES. 557 



complete cessation of movement in the condition of expiratory stand- 

 still. The effect thus produced is similar to, if not identical with, 

 that produced by stimulation of the superior laryngeal nerve. This 

 would seem to indicate the presence in the vagus trunk of two sets 

 of afferent fibers coming from the lungs through the pulmonary 

 branches, one of which inhibits inspiration, the other expiration. 



Faradization of the trunks of the pulmonary branches or stimula- 

 tion of their peripheral terminations in the mucous membrane of 

 the bronchial tubes or alveoli by the inhalation of chemic vapors 

 causes arrest of respiratory movements, a fall of blood-pressure, and 

 a reflex inhibition of the heart (Brodie). 



Gastric Nerves. Stimulation of the peripheral end of a divided 

 vagus nerve causes a distinct contraction of the right half of the 

 stomach and secretion from the gastric glands. Division of the nerve 

 abolishes the sensibility of the mucous membrane of the stomach, 

 impairs motility, and interferes with the secretion of the gastric juice. 



Similar experimentation on the trunk of the vagus has shown that 

 the nerve excites contraction of the upper part of the small intestine 

 and of the gall-bladder, the secretion of the pancreas, the renal cir- 

 culation, the secretion of urine, etc. 



Functions. The afferent fibers transmit nerve impulses from the 

 area of their distribution to the medulla and thence through cortical 

 connections to the sensor cerebral areas, where they evoke sensations. 



The efferent fibers transmit impulses outward which excite con- 

 tr flff 1f >n i^f fr* Tni1gf '^ g of the esophagus, the stomach, the small intes- 

 tine, and the gall-bladder, and the muscles of the bronchial tubes 

 excite secretion from the glands of the stomach, pancreas, and 

 kidney and exert an inhibitor influence on the activity of the 

 heart. The efferent fibers belong to the autonomic system of nerves 

 and are not connected with the ganglia of the vagus, but with local 

 peripheral ganglia. 



ELEVENTH PAIR. THE SPINAL ACCESSORY. 



The eleventh cranial nerve, the spinal accessory, consists of 

 peripherally coursing fibers which bring the nerve-cells from which 

 they arise into relation with separate but functionally related muscles. 

 I^CQnsist_Qf two portions, the medullary or bulbar and the'spinal. 



Origin. IneaSons^mpSKg the medullary portion anseTrom 

 a group of nerve-cells in the lower part of the nucleus ambiguus. 

 From this origin the axons pass forward and outward to emerge from 

 the medulla just below and in series with the roots of the vagus nerve. 



The axons comprising the spinal portion have their origin in 

 nerve-cells in the lateral margin of the anterior horn of the gray 

 matter in the cervical portion of the cord as far down as the fifth 



