CEEEBBAL CONVOLUTIONS — " SALLY." 53 



touch in the median line. In none of the brains which I have 

 examined is this keel absent ; it is present in the '' Sally "-like 

 brain in the Museum of the Royal College of Surgeons referred 

 to above; it was present in the brain described by Miiller. 



A front view of " Sally^s " brain thus presents a great contrast 

 with that of any other chimpanzee hitherto examined, and 

 recalls that of an oraug or man (see figs. 5 — 7). 



Since it is the posterior part of the brain which is so 

 characteristically developed, I will commence with this region. 



4. The Parieto-occipital Fissure. 

 This fissure in " Sally's " brain presents certain features of 

 interest, chiefly in that it is divided into two portions, one of 

 which, the mesial or " internal " parieto-occipital, is confined 

 to the mesial surface ; the other extends on to the upper sur- 

 face of the hemisphere, and may be termed the ''lateral" parieto- 

 occipital fissure, as the term "external" has been used in 

 rather a different sense from that which I wish to indicate here. 

 Viewed from the upper surface (figs. 2, 10), the parieto- 

 occipital on this left side appears as a deep, well-marked fissure 

 about 15 mm. long, extending rather obliquely outwards after 

 coming on to the surface, which it cuts at a distance of 75 mm. 

 from the anterior end. This superior or lateral portion of the 

 parieto-occipital is bounded by an " arcus parieto-occipitalis " 

 (Gratiolet's "secondeplide passage"), which is, as usual, marked 

 out laterally by the ramus occipitalis of the intra-parietal (/?*.) 

 and anteriorly by a small mediad of this branch {n.), the prae- 

 arcal branch. But there is another portion of the parieto- 

 occipital fissure which does not reach the upper surface, and 

 which Beddard overlooked. It is seen in fig. 2 lithographed 

 from a photograph, and also in fig. 10, just in front of the 

 lateral portion. When the mesial surface of the hemisphere is 

 examined (fig. 14), it is seen that the first-named portion of the 

 furrow [lat. p. o.) is nearly entirely cut off from the remaining 

 vertically disposed part of the furrow {mes. p. o.), for the 

 anterior limiting gyrus passes very deeply down at a., and 

 disappears from view, so that the superficial and the vertical 



