nil-; \i;r\ous system 545 



drites of the pyramidal cells. (2) External granular layer, very 

 often termed the layer of small pyramids. The dendrites of the 

 cells of this layer mostly enter the first layer, their axones pass 

 downward into the white matter. (3) Pyramidal layer, often called 

 the layer of superficial medium and large pyramids. This is com- 

 posed principally of typical pyramids sending dendritic branches 

 into the first layer and axones into the white matter. The larger 

 cells are in the deeper part (sublayer of large pyramids). This layer 

 also contains many granule cells with short axones and cells of Marti- 

 notti. (4) Internal granular layer. Here the predominating elements 

 are stellate cells, the larger usually sending their axones into the 

 white matter. Among these are many short axone granules, the 

 axones of which end in the same layer or in more superficial layers. 

 (5) Ganglionic layer or deep layer of large and medium sized pyramids. 

 These send their axones into the white matter. Mingled with them 

 are short axone and ]\Iartinotti cells. (6) Multiform layer or layer 

 of polymorphous cells. These usually send their axones into the 

 white matter. Mingled with them are short axone and Martinotti 

 cells. (Figs. 362, 363 and 364.) 



The cells of the cortex obviously fall into two classes : efferent pro- 

 jection cells and association cells. Which cells are projection cells is 

 not definitely known, except in the case of the precentral motor cor- 

 tex where it has been established that these cells are the cells of Betz, 

 the axones of which form the pyramidal tract and the fibres to 

 motor cranial nerve nuclei. An examination of this area shows that 

 the association cells must enormously outnumber the efferent pro- 

 jection cells in the cortex. The association cells comprise the short 

 axone cells and cells the fibres of which enter the white matter, but 

 terininate in some other part of the cortex, forming the association 

 fibres of the white matter. (Compare p. 539.) 



It is thus evident that every part of the cortex contains termina- 

 tions of association fibres. The areas containing the terminations 

 of afferent projection fibres are those which receive the thalamocorti- 

 cal continuations of the afferent pallial paths and the continuations 

 of the olfactory paths. From observations made with the Golgi 

 method it seems probable that the afferent projection fibres are 

 coarse fibres which may ramify throughout the greater part of the 

 thickness of the cortex, but are confined mainly to the third and 

 fourth layers. The principal areas of the cortex receiving the af- 

 ferent projection fibres are the hippocampal area (olfactory), the cal- 

 35 



