CALLITHRIX JACCHUS, THE MARMOSET 



159 



frontal and temporal regions by the boundary estalilished through the 

 Sylvian fissure. No boundary exists which indicates the actual limits between 

 the parietal and the frontal lobes except the faint indenture already indicated 



FIG. 74. BASE OF BRAIN, CALLITHRIX JACCHUS (MARMOSET). 

 [Actual Length, 29 mm.] 



as the probable inception of the sulcus centralis which, however, is not a 

 constant marking m the marmoset brain. In many species it does not appear 

 at all. As no boundary line exists in the occipital region, it is impossible to 

 describe the limits between the parietal and the occipital lobes. The latter 

 lobe, however, has apparently expanded considerably in its general dimen- 

 sions because the pole of the brain now completely overhangs the cerebellum 

 and assumes more closely the general outline of this region in the higher 

 primates. While it is possible to identify the general topography of the frontal, 

 parietal, temporal and occipital lobes in the brain of marmoset, no reliable 

 landmarks may be established as marking the boundaries of these four great 

 hemispheral divisions. The impression conveyed by the survey of the brain 

 in the Hapalidae is that even if this family has definitely entered the lists of 

 the primate kind, its advance has been a most diffident one. While the hemis- 

 phere shows the general outline characteristic of the primate endbrain, it has 



