358 THE NKHYK SYSTEM 



nerve fibers which convey impulses from the brain 

 and cerebellum to the spinal cord. The anterior 

 portion of the medulla and pons contain pathways 

 for the transmission of volitional efferent nerve 

 impulses from the higher centres in the brain to the 

 spinal cord; the posterior portion contains pathways 

 for the conduction of afferent nerve impulses from 

 the spinal cord to the brain. The medulla and pons 

 contain groups of nerve cells and nerve fibers, called 

 nerve centres, which are in connection with and can 

 be influenced reflexly by other nerve impulses received 

 from associated groups of nerve fibers. 



The Cerebellum. The cerebellum is the largest portion 

 of the hind-brain. It lies in the posterior fossa of the 

 skull separated from the occipital lobes of the cere- 

 brum by the tentorium cerebelli. It is behind the 

 pons and medulla oblongata, connected with the 

 former through the middle peduncles, and partly 

 embracing the latter; and connected with the restiform 

 body (medulla) by means of the inferior peduncles; 

 the superior peduncles contain fibers which pass from 

 the cerebellum to the tegmentum of the rnidbrain in 

 front. 



The cerebellum is divided into a medial segment, 

 the vermis or worm; two lateral hemispheres; a ventral 

 and dorsal notch; and a superior and inferior surface; 

 and is subdivided into lobes and fissures. 



The arbor vitse is the name given to the arrangement 

 of the white substance of the cerebellum, seen on a 

 median section. The cerebellum weighs 5.8 ounces in 

 the male; and 5.4 ounces in the female. The propor- 

 tion between the cerebellum and cerebrum is 1 to 7.5 

 in the adult; 1 to 8.5 among eminent men; 1 to 20 in 

 the newborn. (Gray.) 



The Structure of the Cerebellum. Examined on a 

 cross-section, the cerebellum consists of gray and 

 white matter. The gray matter is external with the 



