432 PHYSIOLOGY 



or ascending frontal convolution, we find below the granular layer the well- 

 marked pyramidal cells or Betz cells, which are larger than any other element 

 in the cerebrum. The layer of pyramidal cells is also very thick, while 



A 



FIG. 224. Human brain showing outer (A) and mesial (B) surfaces, and the situation 

 . of the chief motor and sensory areas. The different shading represents the extent 

 of each of these areas as determined by a study of the histological structure of the 

 cortex. (CAMPBELL.) 



the granular layer is but slightly developed. In this area the actual average 

 thickness of the different layers is as follows : 



Molecular or outer fibre lamina . . . . .0-34 mm. 

 Pyramidal or outer cell lamina . . . . .0-90 mm. 

 Granular or middle cell lamina . . . .0-22 mm. 



Betz or inner fibre lamina ..... O22 mm. 



Polymorphous layer or inner cell lamina , . O31 mm. 



