208 CENTRAL NERVOUS SYSTEM 



which leaves the glossopharyngeal mainly a nerve of motor 

 function. 



X. The afferent fibers of the vagus convey impulses from the 

 pharynx, esophagus, stomach, liver, pancreas, spleen, larynx, 

 bronchi, and lungs. Their termination is near the nceud vital. 

 The functions of the pneumogastrics are very numerous indeed. 

 It is involved in respiration, deglutition, in the movements of 

 the stomach, in the action of the heart, lungs, and viscera. 



XI. The spinal accessory is a motor nerve. It arises by 

 roots from the medulla and from the spinal cord. It supplies 

 the trapezius and sternomastoid muscles so that after section 

 forced respiration is impaired. 



XII. The hypoglossal is a motor nerve. This nerve is 

 important in mastication. In animals its section is followed by 

 inability to drink on account of difficulty in lapping. In man 

 section of the nerve prevents articulation. 



The Medulla Oblongata. In this portion of the brain are 

 situated a great variety of so-called centres. This term implies 

 that any particular physiological action can normally go on only 

 as long as the area of location of the centre in question is intact. 

 The more important of these centres are those which control 

 the circulatory and respiratory organs. If the medulla is sev- 

 ered from the portion of the brain lying anterior to it the animal 

 continues to live for a considerable period. Respiration goes 

 on rhythmically and the bloodvessels retain their tone so as to 

 maintain a normal blood pressure. On the contrary, destruc- 

 tion of the medulla, or of those areas only in which the respira- 

 tory and circulatory centres lie, is followed by a cessation of 

 respiration and a loss of tone in the arteries which result in a 

 rapid death. 



The Cerebellum. An authoritative statement of the functions 

 of this organ is not possible. Flourens advanced the general 

 idea that it serves as a central organ for coordination of volun- 

 tary movements, particularly the more complex movements 

 necessary in equilibrium and locomotion. Luciani regards it 

 as " an organ which by processes that do not awaken conscious- 

 ness exerts a continual strengthening (reenforcing) action upon 

 the activity of all other nerve centres." Sherrington " conceives 

 of the cerebellum as the head ganglion of the proprioceptive 

 system." Lewandowsky has suggested that "normally in 



