MEDULLA OBLONGATA. 115 



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 pyra- 

 mid ; a middle bundle ascends beneath the olivary body, behind the pons, 

 to the cerebrum, as the 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 ex- 

 ternally 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 sensitive 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 con- 

 ductor of coordinating impulses from the cerebellum, through fhe 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. : 



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

 afferent and efferent nerves. (See page 24.) 



2. A centre reflecting impressions which influence the secretion of saliva. 

 (See page 26.) 



3. A centre for sucking, mastication and deglutition, whence are derived 



