CHAPTER X. 



ARCHITECTURE (CONTINUED) : PERIPHERAL NERVES- 

 CENTRAL CELLS CEREBRAL CORTEX. 



Cranial nerves Dorsal and ventral plates of the medullary tube 

 Fissuration Measurements Area of cortex Thickness of 

 cortex. 



IT has been pointed out by the older investigators that 

 as compared with many animals, the cranial nerves in 

 man are small, and that this small size is not only 

 relative, but absolute. So far as these nerves are those 

 of special sense, it might be thought that the diameter 

 of the channel would be important in determining 

 their physiological value. As a matter of fact, compara- 

 tive anatomy does not support this notion, and physio- 

 logy has long since suggested that it is the organisation 

 of the elements which form the central termination of 

 the afferent fibres that is of greatest importance. In this 

 connection is given a chart showing the area in cross- 

 section of all the sensory and motor nerves in man. 



(Fig. 33-) 



Unfortunately there are no adequate observations on 

 animals to compare with these, so that the relations 

 between the areas of the cranial and spinal nerves can- 

 not be contrasted with those in man. 



There yet remains another way of dividing the central 

 system according to certain features shown most clearly 

 during its earlier development. This method of divi- 



