40 



NERVOUS SYSTEM AND GENERAL SENSATION. 



primary course of the cerebral nerves, and their points of union 

 with the brain and medulla obkmgata. 



/ 



Fig. 20. Section of the Brain of Man, shewing the primary course of the 



Nerves. 



[ 86. THE CEREBRUM (a) is in man the most voluminous 

 part of the brain. It occupies all the upper portion of the 

 cranium, from the frontal to the occipital bone (fig. 79). It 

 is of an ovoid form, with the largest extremity directed back- 

 wards. Superiorly and posteriorly it is divided into two 

 hemispheres, separated from each other by a fold of the 

 dura mater, called the falx cerebri, which descends between 

 them. Inferiorly, the hemispheres are limited by a broad 

 band, f, caUed the corpus callosum, which extends its fibrous 

 structure into both hemispheres, and unites them organi- 

 cally together. The surface of the cerebrum presents a num- 

 ber of elevations and depressions, which wind in a tortuous 

 manner, resembling the foldings of the small intestine in the 

 abdomen. These are called the convolutions of the brain, and 

 arise from the great development of the nervous substance 

 being thus folded to pack into a small compass ; the convo- 

 lutions are more or less deep in proportion to the development 

 of the cerebrum. In infancy they are shallow, as well as 



