THE BRAIN AND ITS APPENDAGES. 129 



pearance of their interior ; they receive some important ner- 

 vous trunks in their passage from the brain, and for lodging 

 the terminations of the internal carotid arteries. They com- 

 monly communicate with the sub-occipital sinus ; these are 

 also of membranous formation, and are found upon the cunei- 

 form process of the os occipitis, running longitudinally to the 

 foramen magnum. They receive veins from the cerebellum 

 and posterior parts of the cerebrum. 



Cerebrum. — The largest portion of the cerebral mass, 

 and that which presents itself to our view in raising the skull, 

 is the cerebrum. It is equally divided by a longitudinal fis- 

 sure along its middle, into which the falx cerebri descends ; 

 and its divisions, which are symmetrical, both internally and 

 externally, are denominated hemispheres. 



Cerebellum. — The cerebellum is at once distinguished 

 from the cerebrum by its being only one sixth the size of the 

 latter. Its figure is irregular : it has two oval ends, and its 

 lateral dimensions exceed its longitudinal. It is divided into 

 three oblong lobes — a middle and two lateral. 



Medulla oblongata, the smallest division of the cerebral 

 mass. It rests on the cuneifoim process of the occipital bone, 

 and is continued upward and backward to the foramen 

 magnum. 



The upper surface of the medulla oblongata forms, with 

 the tuber annulare, the floor of the fourth ventricle. 



Pituaiary gland, a red body, of an egg form, seated upon 

 the sella tursica, within a fold of the dura mater. It has 

 a membranous capsule, surrounded by cellular adhesions, by 

 which it is firmly retained in its place. 



Medulla spinalis. — The spinal marrow is that extended 

 portion of brainlike substance which is continued from the 

 posterior part of the medulla oblongata through the entire 

 length of the spinal canal. It is enclosed in the same mem- 

 branes that envelop the brain ; but, in addition to them, the 

 superior ligament of the spine serves as a covering and de- 

 fence to it below. To this, and to the periosteum lining the 

 canal, its proper theca is loosely attached by cellular, adipose, 

 17 



