86 THE GENERAL ANATOMY OF THE LEMUROIDEA [SECT. A 



(iii) Again, the possibility of special adaptations has to be 

 taken into account. Having regard to the nocturnal habits of 

 many Lemurs, the student must be prepared to recognize (and 

 possibly to discount) exuberant development of the parts directly 

 connected with vision and hearing. 



(iv) In such investigations, the absolute size of the animal 

 is a factor of importance. For instance, large animals will be 

 found to possess (ceteris paribus) a higher grade of cortical folding 

 or complexity than smaller forms. 



These considerations will be discussed more fully in a later chapter, but 

 they demand prominence in any comparison of brains. 



With such introductory principles in mind, we may now consider the brain 

 of the Lemur as described in the following paragraphs. 



(a) Rhinencephalon 1 . The olfactory bulbs (Figs. 44 and 45) are of 

 relatively large size and sessile, i.e. in close contact with the brain. The 

 rhinencephalon is separated from the neopallium by a rhinal fissure which 

 varies as regards its distinctness in particular species. 



(6) The marginal pallium is limited by a hippocampal fissure, which is 

 nearly vertical in direction. The uncus, hippocampus major, the sub-splenial 

 gyrus A. Retzii, the fimbria and fornix are all distinct. 



(c) The neopallium is (comparatively) feebly convoluted, and the true 

 Sylvian fissure is present, though only the hindmost part of this fissure, as 

 seen in the higher Primates, is present in the Lemur's brain. The illustrations 

 (Figs. 44, 45) may be consulted for the other sulci. 



(d) In contrast with the conditions obtaining in the higher Primates, the 

 occipital lobe in the Lemurs is usually small, and it therefore fails to overlap 

 much of the cerebellum. The posterior cornu of the lateral ventricle is not 

 present. 



(e) The motor and visual areas of the cortex are extensive. Here we may 

 add that the frontal, temporal and parietal association areas are relatively 

 limited in extent. The distribution of these cortical areas on the neopallium 

 is shewn in Figs. 46 and 47 2 . 



"Limiting" sulci or fissures are represented in these figures by the fissura 

 rhinal is. 



1 These terms are defined in a subsequent chapter. The descriptions are 

 based upon the publications of Professor Elliot Smith mentioned in the footnote on 

 p. 43. 



2 The areas shewn in these charts are those given by Dr Brodmann (Veryleich. 

 Lokalisationslehre der Grosshirnrinde, 1909). They differ in position and extent 

 from those described by Dr Mott (cf. Collected Papers from the Pathological 

 Laboratory of the London County Asylums, 1909, p. 490). 



