PARIETAL REGION IN THE PRIMATE BRAIN 331 



The sulcus occipitalis inferior must now be considered. In 

 Cercopithecus and' indeed in most of the Old World Apes, in which 

 it also goes under the name of occipitalis lateralis or occipito- 

 temporalis lateralis, it bears much the same relation to the striate 

 area as does the lunate and like this is often markedly operculated. 

 This being the case, it cannot be the inferior occipital as we shall 

 use the term for the human brain and the same restrictions wdll be 

 necessary in its application to the Simiidae. The anterior end 

 of the sulcus in Cercopithecus lies within area 19. There develops, 

 however, particularly in the higher Cercopithecidae, a short fur- 

 row parallel with, and at a varying distance in front of, the up- 

 turned end of the inferior occipital, the Querfurche of Zuckerkandl 

 ('04). In its further development it exhibits the tendency to 

 extend backward toward the occipital pole below the inferior 

 occipital or may reach the tentorial surface further forward. It 

 may be found as an apparent dependency of the middle temporal or 

 be broken up into anterior and posterior fragments. Through- 

 out these forms it represents the anterior limit of the preoccipital, 

 area 19. Like the sulcus lunatus there is buried in the upper oper- 

 culated wall of the inferior occipital in these animals, the occipital 

 or parastriate area, 18, and to this wall it is largely restricted since 

 it forms only a narrow zone between areas 17 and 19. The fate 

 which, in many cases in man, overtakes the lunate is shared to 

 even a greater extent and appears phylogenetically much earlier in 

 the case of the inferior occipital. 



It is fascinating to follow the life history and vicissitudes of 

 the lunate and its operculum in the Primate brain. From its 

 first and inconstant appearance in relatively simple form in the 

 Lemurs, it pushes itself rapidly forward, driven by the increas- 

 ing striate cortex behind, which far surpasses any other area in 

 extent and rate of growth; not until there are submerged under 

 the advancing operculum the major parts of the occipital and pre- 

 occipital areas, whose cortex already begins to show various fur- 

 rows, and until it has reached the enormous dimensions in Cer- 

 copithecus and Cynocephalus is there anything encountered to 

 stay its progress. From this point it begins to decline and recede, 

 owing not only to a reduction in the extent of striate cortex but 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 24, NO 3 



