446 PHYSIOLOGICAL SERIES. 



ends near the inferior limb of the Y-shaped lateral occipital 

 sulcus. 



At the bend of the retrocalcarine a second postcalcarine 

 snlcus appears to emerge from the former and then run 

 parallel to and on the dorsal side of it. It is separated 

 from the ventral postcalcarine by a gyms which is sub- 

 merged at its anterior end. The dorsal postcalcarine sulcus 

 is much shallower and more widely separated from the 

 calcarine complex on the right side. 



The parieto-occipital snlcns is a deep and well-defined 

 sulcas on the right hemisphere, and there are also several 

 small accessory sulci. On the left hemisphere the suleus is 

 represented by three snlci of varying depths. The meaning 

 of these separate snlci will be best appreciated if the 

 reader refers to the acconnt of the Baboon's brain. There 

 is, first, a deep irregnlar notch in the upper margin of the 

 hemisphere, which represents the sulcns distinguished as 

 the raraus parieto-occipitalis (sulci intraparietalis) in the 

 larger Cercopithecidae, There is a very deep sulcus on 

 the mesial surface, which begins above in front of the 

 last-described element and ends near and parallel to the 

 calcarine sulcus, to which it is joined by a shallow connecting 

 furrow. Then there is a third shallower furrow making (on 

 the surface) a Y-shaped pattern with the last. Tb 

 limbs of the Y are separated from the first (" ranius par.- 

 occ. s. intrap.") element by a plump arcuate gyrus. If the 

 other Gorilla-brains be examined, further variations of 

 the calcarine and parieto-occipital systems will be found. 

 Thus in specimen D. 659 the calcarine complex is T-shaped 

 in both hemispheres ; in specimen D. 660 the calcarine 

 and retrocalcarine unite at an obtuse angle and small 

 compensatory sulci surround the latter. All this shows 

 that the true calcarine (Cunningham's " anterior calearine ") 

 is the only stable element in the calcarine series and the 

 retrocalcarine (Cunningham's " 4 posterior calcarine ") series 

 is extremely variable, although the chief sulcus is always 

 concurrent with the calcarine. 



The parieto-occipital series, being essentially of the 

 nature of compensatory sulci, is even more variable. In 

 specimen D. 659 the state of affairs is essentially identical 



