THE ENCEPHALON 25! 



7. Special Centers. In the gray matter of the cord are 

 found various centers for distinct acts such as defecation, 

 parturition, micturition, etc. These are all connected with 

 each other and with the encephalon and obey the usual laws 

 of reflex action. 



THE ENCEPHALON. 



The encephalon is situated within the cranial cavity and 

 is commonly called. the brain. Its gross divisions are the 

 medulla oblongata, the pons Varolii, the cerebellum, and the 

 cerebrum. All the other divisions are in a measure subordi- 

 nate to the cerebrum, though each division has individual 

 functions. The human brain weighs about 49^/2 ounces in 

 the male and about 44 in the female. 



The Medulla Oblongata. 



Anatomy. The medulla oblongata, or bulb, joins the 

 upper extremity of the spinal cord and extends to the pons 

 above. It has a pyramidal shape, lies in the basilar groove 

 of the occipital bone, and is slightly flattened antero-poster- 

 iorly. It is about an inch and a quarter in length, half an 

 inch thick, and three-quarters of an inch broad above. The 

 anterior and posterior median fissures of the cord are con- 

 tirmed upward in the medulla ; the central canal terminates 

 in the inferior angle of the fourth ventricle. The anterior 

 columns appear to be continuous with the anterior pyramids 

 of the medulla. These pyramids are situated just lateral to 

 the anterior median fissure. The innermost fibers of the 

 pyramids are the continuations upward of the crossed pyra- 

 midal tracts, and are seen to decussate in the median line ; 

 the outermost fibers are the prolongations of the uncrossed 

 pyramidal tracts. The olivary bodies, oval in shape, are 

 just external to the anterior pyramids separated from them 

 by a groove. The restiform bodies make up the postero- 



