486 THE NERVOUS SYSTEM. 



from the direct pyramidal tracts of the same side, while the decus- 

 sation consists of the libers of the crossed pyramidal tract of the 

 lateral column. 



In the restiform bodies are to be found, besides the funiculus 

 of Rolando and the funiculus cuneatus, fibers of the direct cere- 

 bellar tract of the lateral column. These bodies form the inferior 

 peduncles of the cerebellum. The funiculus of Rolando is the 

 enlarged head of the posterior cornu of the cord, and is therefore 

 gray matter. The funiculus cuneatus is the continuation of 

 Burdach's column of the cord, and the funiculus gracilis is the 

 continuation of GolPs column. 



Functions of the Medulla Oblongata. Conduction. All the 

 impulses, whether afferent or efferent, passing between the brain 

 and the cord must pass through the medulla. 



Nerve-centers. Experiments have demonstrated that all the 

 brain above the medulla and all the spinal cord may be removed 

 and yet life be maintained, provided that the origin of the phrenic 

 nerves is left intact; while if all these structures are undisturbed 

 and the medulla is destroyed, death will result. The centers in 

 the medulla are both reflex and automatic. 



Reflex Centers. One of the most important of these centers is 

 that which presides over deglutition. As has been seen in dis- 

 cussing this process, the first stage of the act is voluntary ; but 

 as soon as the food has passed into the pharynx, the act becomes 

 involuntary. The mucous membrane of the pharynx is stimu- 

 lated by the food, and the afferent fibers of the glossopharyngeal 

 transmit the impulse to the medulla, in which a motor impulse is 

 generated, and out along the efferent fibers comes the impulse to 

 the constrictors of the pharynx. Centers for vomiting, coughing, 

 sucking, and for other movements are described. 



The act of vomiting is a reflex one, in which the fibers of the 

 pneumogastric serve as afferent fibers, the impulses stimulating 

 the center in the medulla, from which emanate motor impulses 

 to the respiratory and other muscles concerned in the act. If the 

 act of vomiting is brought on by stimulating the pharynx with a 

 feather or with a finger, the glossopharyngeal is the carrier of the 

 afferent impulses. Afferent impulses producing vomiting may also 

 come from other organs, such as the kidneys, or the testicles when 

 injured. 



Central Vomiting. In central vomiting the center is stimu- 

 lated by impulses which come from the cerebrum. 



^ Merycism, or Rumination. The power to ruminate, by virtue 

 of which animals chew the cud, is possessed by some human in- 

 dividuals, who can regurgitate the food whenever they feel so 

 disposed, and chew it again. 



Automatic Centers. Besides reflex centers, which require a 

 stimulus from without to bring them into action, the medulla 



