MORPHOLOGY OF THE BRAIX IX THE MAMMALIA. 347 



The typical calcarine group of sulci closely resembles that already described ia Nucll- 

 cebus. There is a simple linear intercalary sulcus above the anterior two-thirds of the 

 corpus callosum. In one brain there is also a very small oblique rostral sulcus placed far 

 forward on the mesial surface of the hemisphere. 



The hippocami)al formation presents the typical features, with a large hippocampal 

 tuliercle and distinct circumsplenial vestiges. 



The cerebral hemisphere is 30-5 mm. long, and its posterior extremity is drawn out 

 into a distinct caudal (or occipital) process. The corpus callosum is 13-5 mm. long, and 

 its splenium is 11 mm. in front of the occipital pole of the hemisphere. The maximum 

 depth of the hemisphere is 195 mm. 



Althougli the brain of Galago vrassicaudata is only a little larger tlian that of 

 Garnett's species, there is a noteworthy increase in the number and extent of the sulci. 

 This fact becomes more interesting and significant when it is observed that the pattern 

 mapped out by the new sulci is identical with that found in the genus Lemur. 



The characters of the cerebral hemisphere of the Great Galago may thus be summed up 

 by saying that it is a brain of the same shape as (although slightly larger than) that of 

 Garnett's Galago, with the sulcal pattern of a Lemur. 



The upper extremity of the Sylvian fissure bends slightly backward and approaches the 

 upper end of the postsylvian sulcus, as so often happens in the genus Lemur. The post- 

 sylvian sulcus is represented in the brain in the Royal College of Surgeons merely by a 



G(iJ(ir/() crassicdidhitu. 

 I.aleiiil aspect of tbo left cerebral hemisphere. Xat. size. 



short furrow corresponding to its upper end, whereas in Beddard's specimen* it is the lower 

 end of the sulcus which is deepest. In the skulls of this species which I examined 

 there was a low ridge representing a sulcus as extensive, though not so deep, as that of 

 Lemur. The postsylvian sulcus must be regarded as poorly developed in all the 

 Galaginae. Another instance of this has already been seen in the genus Lepklolemxr. 



In Beddard's specimen the lateral sulcus (which he calls "angular") is represented as 

 a short linear furrow, like that of Garnett's Gtilago. But in the actual brain (and 

 also in a skull of this species labelled " Otogale Kirkil " in the British Museum) i have 

 found evidence of a much more extensive arcuate lateral sulcus surrounding the upper end 

 of the Sylvian fissure. In the brain in the Royal College of Surgeons the posterior end 

 of this sulcus is bent mesially ; and at a short distance behind it there are Iavo shallow 



* Proc. Zool. Soc. 1895, p. 14G, fig. 4. 



