CEHEHRAL CORTEX. 291 



cortex of the temporal lobe through the medial geniculate 

 body and the internal capsule. 



The sensory path of the facial, nerve that is, the pars inter- 

 medius is riot known. 



The fibres of the optic nerve enter the brain in the region 

 of the thalamus. A part of the fibres pass downward into the 

 border of the superior colliculus; the rest enter the internal 

 capsule just posterior to the pyramidal tract fibres and pass out 

 to the occipital lobe. The fibres of the olfactory nerve have no 

 direct connection with the brain-stem. They enter the olfac- 

 tory bulb, beneath the frontal lobe, and pass to the cortex of 

 the frontal and temporal lobes. 



Only a small part of the cortex of the brain represents the 

 nerves of the body. In general, the area around the fissure of 

 Rolando receives sensory impressions from the entire body and 

 sends out the fibres of voluntary control. The special senses 

 are represented as follows : sight, in a small part of the occipital 

 lobe ; hearing, in a part of the temporal lobe ; and smell, in a 

 part of the temporal and frontal lobes. All the rest of the 

 cortex is the " great silent area," or the association centres of 

 the brain. These areas are connected richly by fibres both 

 with the same side and with the opposite side of the brain. 

 These are the association paths which make the brain the organ 

 of thought. 



C. Cerebral Cortex. 



The cerebral cortex shows certain differences in structure in 

 different regions, into the details of which we cannot here enter. 

 All regions have a structure which conforms to one type, which 

 will be described. The cortex consists of gray substance in 

 which four layers can be recognized. These pass over into 

 one another without sharp boundaries (Figs. 218 and 219). 

 Beginning at the outside, we meet with the following structures : 



1. The Molecular Layer (Stratum Zonale}. This is a layer 

 which is poor in cells, but shows a finely granular and reticular 

 structure. This is due partly to the interlacing dendrites and 

 axones of nerve cells whose bodies are situated more deeply, but 



