18 



Mr. W. B. Lewis. On the 



[Nov. 17, 



6. Fxtra-limbic Type. — Area. This cortex covers the whole of the 

 extra- limbic or parietal mass, except that portion already referred to 

 as possessing the upper and modified limbic types. — Type. It is 

 distinctly five laminated, viz.: — 1. A peripheral zone; 2. Layer of 

 small pyramids ; 3. Belt of granule cells ; 4. Ganglionic cells ; 

 5. Spindle cells. It differs from the npper limbic type in the 

 possession of a belt of grannie cells, and in the peculiar disposition of 

 its ganglionic cells which, lose the clustered and assume a solitary 

 arrangement. 



The ganglionic cells become more and more numerous and thickly 

 grouped towards the frontal pole, diminishing in numbers rapidly 

 backwards, the granule cells being a more notable feature towards 

 the occipital pole. 



Significance of Sulci and Fissures. — In my former memoir I stated 

 that certain sulci and fissures accurately mapped out structurally 

 differentiated realms of the cortex. My further examination of the 

 brain of the rat and rabbit enables me to state that at least seven sulci 

 and fissures may now be accepted as the undoubted boundaries of 

 adjacent realms which wholly differ from each other in structure. These 

 are as follows : — 



1. The limbic fissure. 



2. The infra-parietal sulcus. 



?>. The primary parietal sulcus. 



4. The inter-parietal sulcus. 



5. The crucial sulcus. 



6. The olfactory sulcus. 



7. Fissure of Rolando. 



Distribution, of Ganglionic Formation. — The cortex, which is specially 

 characterised by a rich deep belt of ganglionic cells in close confluent 

 groups, spreads over that portion of the upper limbic arc immediately 

 in front of the corpus callosum. Still richer in constituent elements, 

 towards the marginal or sagittal border ot the hemisphere it covers 

 the exposed aspect here, being well developed over the three areas 

 mapped out by Ferrier as the centres for the movements of the mouth 

 and jaws (7) ; of the tongue (9) ; and of the shoulder and 

 foreleg (5). 



Along the sagittal border of the hemisphere at the vertex these 

 rich cell groupings tend to spread backwards, but thin out rapidly as 

 they approach the granule formation internal to the primary parietal 

 sulcus. 



The same tendency to extension of these ganglionic groups back- 

 wards is also seen along the Sylvian border of the hemisphere, i.e., 

 along the limbic sulcus. 



I have therefore termed these groupings the Sagittal and Sylvian 

 groups of the ganglionic formation. 



