198 The Vertebrate Organ Systems 



creased by a series of folds which give it a wrinkled appearance. These 

 folds or elevations are known as gyri and are separated by slight depres- 

 sions, sulci. . Certain sections of the cortex can be shown to be concerned 

 with voluntary muscular activity. Electrical stimulation of a specific por- 

 tion will result in certain definite movements. Due to this specificity of 

 control, various motor areas can be mapped on the cortex. The mus- 

 cular control is always to the opposite side of the body; thus, stimula- 

 tion of the left side of the brain will bring about movements of the 

 voluntary muscles of the right side of the body. 



Cortex of Cerebrum 

 \ 

 \ 



Corpus callosum 



Third ventricle 



Pineal body or gland 

 \ 



Corpora 

 quadijeeniin.i 



Foramen of Monro 



Medullary- 

 center (white 

 matter) of the 



cerebellum 



\ \ 



Pons varolii N 



Fourth ventricle 



'Medulla oblongata 



Optic commissure or 

 chiasma 



■^Infundibulum 



Pituitary body 



Fig. 60. — Left half of human brain. (From Guyer: Animal Biology, 



Harper & Brothers.) 



In its functioning, the cortex is extremely complex. In its complex- 

 ity, it can only be compared to the central switchboard of a very large 

 community where there are innumerable incoming and outgoing calls 

 which must be connected and interconnected. For the transference 

 of information from one center to another, there are many nerve path- 

 ways composed of white matter which are large numbers of nerve cell 

 processes. Chief of these is the corpus callosum, a broad band which 

 connects the two cerebral hemispheres. This structure is found only in 

 the mammalian brain. Ventrally the corpus striatum forms most of 

 the ventral floor of the telencephalon and provides connections with 



