ANATOMY AND PHYSIOLOGY OF THE BRAIN. 423 



ever, leads to its being affected by many other causes, and 

 a sudden full inspiration results, as every one knows, from 

 tue sudden contact of the surface of the body with cold 

 water. Even the normal respiratory movement does not 

 depend on the pneumogastric nerves alone, since, when 

 both these nerves have been divided, a slow and irregular 

 breathing is still kept up. 



Some influence may be exerted by the spinal cord over 

 the muscles of respiration, which supply the trunk, since 

 Richardson and Brown-Sequard mention that they have 

 noticed the respiratory movements in newly-born mammals 

 after the oblong medulla had been entirely removed. There 

 can be no doubt, however, that the action of other parts is 

 almost, if not entirely, subsidiary. Thus, if the whole brain 

 be removed, care being taken not to injure the medulla, 

 life may continue for a considerable time, and respiration 

 may continue uninterrupted. A complete division of the 

 spinal cord at the lower end of the neck paralyzes the 

 thoracic muscles, so that the movements of the thorax are 

 thereafter continued only by the diaphragm. Again, section 

 of the cord in the upper part of the neck paralyzes the 

 latter, and breathing is at once arrested. Eespiratory 

 movements of the face may still take place, but none what- 

 ever in the body. 



Flourens has attributed to a small nucleus of grey matter, 

 lodged in the floor of the fourth ventricle, and close in front 

 of the point where the posterior pyramids diverge from 

 each other, the function of presiding over respiration, and 

 to some extent over the movements of the heart. The 

 nucleus in question he called the vital point, from the 

 circumstance that when it was pricked or otherwise irri- 

 tated, respiration was at once arrested, and frequently the 

 action of the heart ceased as suddenly. Brown-Sequard 



