LEPUS CUNICULUS 349 



and perhaps also with taste. This portion is designated the olfactory 

 pallium or archi-pallium. In lower vertebrates, for example 

 Scyllium and Rana, the archi-pallium forms practically the entire 

 bulk of the fore- brain. As we have seen in the mammal, that is 

 the higher mammal, the remaining part of the pallium, lateral, dorsal 

 and dorsal-mesial in position is even larger than the other. Since 

 it is the part that has been added to the old olfactory pallium during 

 the course of evolution, and is particularly characteristic of the 

 latest group, the Mammalia, it is termed the neo-pallium. It is 

 very highly developed and concerned with visual, auditory and 

 general body sensations, and the voluntary actions connected 

 therewith. It is also the seat of the higher mental processes, and in 

 man is the seat of the mind. These various activities are not 

 diffused generally through the neo-pallial cortex, but are more or 

 less definitely localised in certain definite regions, the so-called 

 sensory areas. For example, along the dorsal region of the hemi- 

 sphere from before backwards, we find areas for the larynx, face, 

 arm, trunk, leg, tail and anus. . On the lateral surface are distinct 

 areas concerned with mastication, oculo-motor and auris centres, 

 and in man there is a speech centre and other regions concerned with 

 association and correlation. To this highly-specialised neo-pallial 

 cortex the mammal owes its great mental powers, which, as has 

 been pointed out, are in the main responsible for its dominating 

 position, and this development and differentiation reach their 

 highest point in man himself. 



The third ventricle is a deep vertical cleft lying in the 

 thalamencephalon, and so being the modified embryonic fore-brain 

 vesicle. It is bounded at the front end by the anterior pillars of the 

 fornix and the lamina terminalis, including the anterior commissure 

 and the posterior portion of the septum lucidum. On each side of 

 the latter are the foramina inter vent ricularia, putting the third 

 ventricle in communication with the lateral ventricles. Posteriorly 

 it is much reduced and continued backwards as the iter. The side 

 walls are furnished by the optic thalami. Its floor is formed by the 

 optic chiasma, the tuber cinereum, the corpus mammiUare and the 

 part of grey matter of the posterior perforated spot. The roof is 

 very thin, being composed of ependymal epithelium, and imme- 

 diately above it a double fold of vascular pia mater runs forward 

 some distance under the hinder ends of the hemispheres as the 

 velum interpositum. This fold of the pia mater pushes the roof 

 down on the two sides to form the anteiior choroid plexuses, which 

 thus project into the ventricular cavity. Anteriorly these plexuses 

 become continuous through the interventricular foramina with 

 those of the lateral ventricles. At each side of the middle line, the 



