194 HUMAN PHYSIOLOGY. 



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 fibers 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 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 externally and gray matter internally, 

 forming the corpus dentatum. 



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

 the cord, also receives fibers from the lateral column. As the 

 restiform bodies pass upward they diverge and form a space (the 

 fourth 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 trans- 

 verse commissure is exposed, forming part of the floor of the 

 fourth 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 



1. As a conductor of afferent or sensor impulses upward from the 

 cord, through the gray matter to the cerebrum. 



2. As a conductor of efferent, volitional or motor impulses from the 

 brain to the spinal cord and nerves, through its anterior pyramids. 



3. As a conductor of coordinating impulses from the spinal cord to 

 the cerebellum, through the restiform bodies. 



As an Independent Reflex Center. The medulla oblongata con- 

 tains special collections of gray matter, constituting independent 



