854 THE CENTRAL NERVOUS SYSTEM 



tex in different parts of the normal brain with that found in the brain 

 of psychopathic individuals whose mental symptoms have been care- 

 fully studied before death.* 



For the purpose of this work it is necessary to recognize several 

 laminae or layers of nerve cells and nerve fibers composing the cortex. 

 The most practical division is represented in Fig. 220, and is as follows: 

 (1) a narrow superficial layer of nerve fibers, with a few scattered cells 

 the outer fiber lamina or molecular layer; (2) a much wider layer of small, 

 medium and large pyramidal cells the outer or pyramidal cell lamina ; 

 (3) a layer of granules the middle cell lamina; (4) an inner layer 

 of nerve fibers, sometimes containing large solitary cells (Betz cells) 

 the inner fiber lamina; (5) a layer of polymorphic cells the inner cell 

 lamina. This five-layer type undergoes structural modifications in the 

 different regions of the cortex, and these modifications possess a dis- 

 tinct functional significance. The only part of the brain in Avhich they 

 can not be recognized is the hippocampus and the pyriform lobe. Based 

 on the relative thickness of these layers maps of the cerebral cortex 

 have been produced. The most important are those of Brodmann and 

 Campbell, of which the latter is reproduced in Fig. 221. Two re- 

 gions can be very definitely located; namely, the precentral or Betz- 

 cell area, and the visual or visuosensory area of Campbell. Surrounding 

 the visuosensory area is a definite visuopsychic area, and similarly, 

 bordering on the precentral is the so-called intermediate precentral 

 area. At the very front of the frontal lobe is the prefrontal area. Post- 

 central and intermediate postcentral areas are indicated, but the re- 

 mainder of the center is undefined. 



Reasoning from phylogenetic and ontogenetic data, we can assign to 

 each of these laminae a functional significance, which according to Bol- 

 ton is as follows: The outer cell lamina (pyramidal cell lamina) proba- 

 bly constitutes the "higher level" basis for the carrying on of the higher 

 or psychic cerebral functions. It is a prominent, feature of the human 

 cortex, the last cell layer to be evolved, and the one which undergoes 

 retrogression most readily. During development it rapidly attains ma- 

 turity in the visuosensory area, next in the visuopsychic, and only later 

 in the prefrontal region. In the visuopsychic area it is practically of 

 the same depth as in the visuosensory, whereas in the prefrontal region it 

 develops according to the mental capacity of the animal. In patients ex- 

 hibiting symptoms of dementia this layer of cells is distinctly deficient. 

 These facts indicate that the outer or pyramidal cell lamina "subserves 

 the psychic or associational functions of the cerebrum" (Bolton). 



*An excellent account of the physiologic basis for such work is given by Bolton in Leonard Hill's 

 Further Advances in Physiology. We have made free use of this article in the present review anrl 

 would strongly recommend its perusal by any who may desire further information. 19 



