THE NERVOUS SYSTEM 21 3 



The corpus striatum is a layer of white and gray matter ; 

 the under part corresponds with the convolutions at the 

 base of the brain, known as the island of ReiL 



The tubercula, or corpora quadrigemina, are four rounded 

 eminences, situated two on each side behind the pineal 

 gland; they consist of white and gray matter; the gray 

 matter of the anterior pair giving off the optic nerve, 

 which pierces the ball of the eye ; hence they are sometimes 

 termed the optic lobes. 



The cerebellum is situated in the occipital fossa, below 

 the posterior lobes of the cerebrum. It is elliptic, its 

 broad diameter being transverse. Upon transverse sec- 

 tion it presents an appearance resembling the branches of 

 a tree; hence, as has been stated elsewhere, it has been 

 termed the arbor vita, or "tree of life." It is considered 

 to be more complex in its anatomic arrangement than any 

 other part of the body. 



The pons Varolii is situated at the base of the brain, 

 just above the medulla oblongata, and rests upon the 

 basilar surface of the occipital bone. It has a diameter of 

 about i inch. The basilar artery runs in a groove upon 

 its inferior surface. 



The medulla oblongata is that part of the central 

 cerebrospinal axis that connects the cerebrum with the 

 spinal cord, it is also connected with the cerebellum by 

 the restiform bodies. It is one of the most important 

 divisions of the nervous system, and contains the nerve - 

 centers for speech, deglutition, and respiration. Injury 

 to this structure is, indeed, fatal. 



The medulla oblongata is about i J inches long, and lies 

 above the basilar groove of the occipital bone; it passes 

 backward through the foramen magnum, at which level 

 the spinal cord begins. 



It is divided into anterior pyramids which are continu- 

 ous with the spinal cord on the anterior of the same; 



