STRUCTURE OF THE NERVOUS SYSTEM 



289 



area by the presence everywhere of ridge-like convolutions, 

 between which are deep but narrow depressions, called 

 fissures. The interior of the 

 cerebrum consists mainly of 

 nerve fibers, or axons, which give 

 it a whitish appearance. These 

 fibers connect with the cell- 

 bodies in the cortex (Fig. 131). 



The cerebrum is a double 

 organ, consisting of two similar 

 divisions, called the cerebral 

 hemispheres. These are sepa- 

 rated by a deep groove, extend- 

 ing from the front to the back 

 of the brain, known as the 

 median fissure. The hemi- 

 spheres, however, are closely 

 connected by a great band of 

 underlying nerve fibers, called 

 the corpus callosum. 



At the base of the cerebrum three FlG - 131- Microscope draw- 

 large masses of cell-bodies are to be g f a neuron from cerebral 

 found. One of these, a double mass, cortex - * short *egment f 

 occupies a central position between the the axis c >' linder with collateral 

 hemispheres, and is called the optic branches - 



thalami. The other two occupy front central positions at the base of 

 either hemisphere, and are known as the corpora striata, or the striate 

 bodies. 



The Midbrain is a short, rounded, and compact body 

 that lies immediately beneath the cerebrum, and connects 



proper cell-body, axis cylinder, and dendrites has a grayish color, while the 

 coverings of most of the fibers are white. Hence gray matter in any part of the 

 nervous system indicates the presence of cell-bodies, and white matter the presence 

 of nr rve fibers. 



