386 PHYSIOLOGICAL SERIES. 



of the cerebral hemisphere has taken place so as to com- 

 pletely cover the flattened cerebellum. The extent of this 

 backward growth is most strikingly shown upon the mesial 

 surface (fig. 226): almost half of the hemisphere lies behind 

 the situation of the splenium of the corpus callosum (fi<js. 

 224 & 225). 



Upon the cranial surface the Sylvian fissure will be 

 seen to have fused with the intraparietal sulcus, as in 

 Nycticelus ; and the sulcus has even become prolonged 

 on to the mesial surface (fig. 226) where it runs parallel 

 and in close proximity to a new sulcus the parieto-occipital 

 of Human Anatomy. So close are these two sulci that they 

 appear to become concurrent, but if the lips of the common 

 cleft be separated the condition represented in fig. 226 is 

 found *. An elongated parallel sulcus is present. In front 

 of the Sylvio-intraparietal complex there is a short trans- 

 verse sulcus on the dorsal surface (fig. 224), which may be 

 the earliest Primate form of the central (Rolando's) sulcus. 

 On the other hand, it may represent part of the intraparietal 

 sulcus which has not joined the Sylvian fissure. 



As a result of the pronounced caudal elongation of the 

 hemisphere the calcarine sulcus becomes almost horizontal: 

 it ends posteriorly by joining a great vertically transverse 

 sulcus f? which must be regarded as analogous to the retro- 

 calcarine sulcus of other mammalian Orders. AJS a result 

 of the altered mechanical conditions, a series of new com- 

 pensatory-calcarine sulci make their appearance. By 

 reason of its altered direction, the calcarine sulcus is not 

 extended downward to the neighbourhood of the rhinal 

 fissure, as in most mammals, and a ventral compensatory 

 sulcus the " collateral " of Human Anatomy develops 

 to make good this defect. It appears in this case to join 

 the calcarine, but is in reality separated from it by a sub- 

 merged gyrus (fig. 226). A vertical compensatory sulcus 

 makes its appearance on the dorsal side of the calcarine and 



* In reality the parieto-occipital sulcus represents the fusion of two 

 separate sulci. In this case the dorsal of these two fundamental elements is 

 concurrent with the intraparietal sulci. 



t Perhaps it would be more correct to say that it joins the stem of a 

 T-shaped postcalcarine sulcus. 



