X Journal of Comparative Neurology. 



The intra-parietal sulcus. 



" I. The entire sulcus, single and continuous in some of the 

 lower apes (e. g. Cebus), becomes broken up in the human brain into 

 a group of furrows which present different relations to each other in 

 different cases. 



2. Three of the elements of the sulcus in the human brain, viz: 

 the sulcus postcentralis inferior, the ramus horizontalis, and the ramus 

 occipitalis, are disrupted portions of the original fissure; one, the sul- 

 cus post-centralis superior, is a superadded element. 



3. In the development of the sulcus in the human foetal brain 

 all the four segments of the sulcus have, as a rule, an independent 

 origin, although, as Pausch has shown, the sulcus postcentralis infe- 

 rior and the sulcus horizontalis very frequently appear as one contin- 

 uous furrow. 



4. The sulcus postcentralis inferior usually appears first ; then 

 the ramus horizontalis and ramus occipitalis ; and last of all the sulcus 

 postcentralis superior. 



5. In Cebus there is no sulcus postcentralis superior, it is 

 present, however, in most of the old world apes, e. g. the baboon, 

 macaque, gibbon, chimpanzee, orang, and gorilla. 



6. In the chimpanzee and orang there is reason to believe that 

 this segment of the postcentral sulcus consists of two elements, one 

 placed above the other. 



7. Eberstaller's third and lowest segment of the postcentral 

 sulcus (viz. the sulcus postcentralis transversus) is not only present 

 in man but also in the majority of the old world apes. 



8. In the apes the intraparietal sulcus is deeper than the fissure 

 of Rolando, the opposite is the case in man. This would seem to 

 indicate that the morphological value of the sulci is different in man 

 and the apes. The phylogeny and ontogeny of these furrows are in 

 apparent variance with each other. The fissure of Rolando appears 

 first on the developing cerebrum of the human foetus, yet it is the 

 intraparietal sulcus which first makes its appearance in the evolution 

 of the primate cerebrum." * * * 



"11. In man there appears to be a general tendency toward a 

 union of the two originally distinct postcentral elements of the sulcus 

 and a divorce from the lower of these of the ramus horizontalis." * * 



"13. The ramus occipitalis was connected with the ramus hori- 

 zontalis in 63.7 per cent, of the adult human hemispheres examined. 



