128 HUMAN PHYSIOLOGY. 



united fibres then pass upward through the pons Varolii and crura cerebri, 

 and for the most part terminate in the corpus striatum and cerebrum. 



2. The lateral tract is continuous with the lateral columns of the cord ; 

 its fibres in passing upward take three directions, viz. ; an external bundle 

 joins the restiform body, and passes into the cerebellum ; an internal bundle 

 decussates at the median line and joins the opposite anterior pyramid ; a 

 middle bundle ascends beneath the olivary body, behind the pons, to the 

 cerebrum, as \\~\o. fasciculus teres. 



The olivary body of each side is an oval mass, situated between the 

 anterior pyramid and restiform body ; it is composed of white matter exter- 

 nally and gray matter internally, forming the corpus dentatum. 



3. The restiform body, continuous with the posterior column of the cord, 

 also receives fibres from the lateral column. As the restiform bodies pass 

 upward they diverge and form a space, the 4th ventricle, the floor of 

 which is formed by gray matter, and then turn backward and enter the 

 cerebellum. 



4. The posterior pyramid is a narrow, white cord bordering the posterior 

 median fissure; it is continued upward, in connection with the fasciculus 

 teres , to the cerebrum. 



The Gray Matter of the medulla is continuous with that of the cord. 

 It is arranged with much less regularity, becoming blended with the white 

 matter of the different columns, with the exception of the anterior. By the 

 separation of the posterior columns, the transverse commissure is exposed, 

 forming part of the floor of the 4th ventricle; special collections of gray 

 matter are found in the posterior portions of the medulla, connected with 

 the roots of origin of different cranial nerves. 



Properties and Functions. The medulla is excitable anteriorly, and 

 sensitive posteriorly to direct irritation. It serves (i) as a conductor of sen- 

 sitive impressions upward from the cord, through the gray matter to the 

 cerebrum ; (2) as a conductor of voluntary impulses from the brain to the 

 spinal cord and ^nerves, through its anterior pyramids; (3) as a conductor 

 of coordinating impulses from the cerebellum, through the restiform bodies 

 to the spinal cord. 



As an Independent Reflex Centre. The medulla oblongata con- 

 tains special collections of gray matter, which constitute independent 

 nerve centres which preside over different functions, some of which are as 

 follows, viz. : 



I. A centre which controls the movements of mastication, through 

 afferent and efferent nerves. (See page 25.) 



