THE NERVOUS SYSTEM. 



439- 



remarkable decuxsation, easily seen by gently separating the sides of 

 the anterior median fissure, formed by distinct bundles of white sub- 

 stance crossing the median line obliquely, from below upward and from 

 side to side. Thus the right anterior pyramid is formed of fibres which 

 come from the left side of the cord, and the left anterior pyramid of 

 those which come from the right side of the cord. 



Fig. 152. 



MEDULLA OBLONGATA AND BASE OF THB BRAIN IN MAN Anterior view. 

 1. Decussation of the optic nerves. 2,2. Middle lobes of the cerebrum. 3, 3. (Jrura cerebri. 

 4. Tuber annulare. 5,6. Lateral lobos of the cerebellum. 6. Anterior pyramid. 7. Olivary 

 body. 8. Eestiform body. (Hirschfeld.) 



Immediate!} 7 ' outside of the pyramids, in a lateral direction, are two 

 elongated oval masses, the olivary bodies, whicli consist externally of 

 white substance, but internally contain each a distinct thin convoluted 

 layer of gray substance, resembling in miniature the convolutions of the 

 cerebrum. The olivary bodies are, therefore, special deposits of gray 

 substance in the anterior portion of the medulla oblongata, superadded 

 to the rest and not continuous with that of the spinal cord. 



At the upper limit of the medulla oblongata is the tuber annulare, so 

 called because it forms a ring-like protuberance at this part of the base 

 )f the brain. Superficially, when viewed in front, it consists of trans- 

 verse bundles of white substance, containing fibres passing over, in an 

 arched form, from one side of the cerebellum to the other, and decus- 

 sating with each other at the median line. Where they cross the tuber annu- 

 lare these fibres constitute the " pons Varolii ;" at the two sides, where 

 they pass backward to the cerebellum, they form the " middle peduncles 

 )f the cerebellum." 



