PARIETAL REGION IN THE PRIMATE BRAIN 305 



sulcus in the simian brain which is the real derivative of the in- 

 ferior occipital of the Cercopithecidae I shall use the term sub- 

 lunate which name might be applied with equal propriety to the 

 inferior occipital of lower forms and the last mentioned term in 

 turn be reserved for the newer fissure of the Simiidae. 



The sulcus temporalis medius is represented by a varying ar- 

 rangement of short shallow furrows, running in various directions, 

 below, but in general parallel with the superior temporal. One 

 of these furrows we shall meet again since it assumes considerable 

 importance. 



The large expanse of cortex situated behind the sulcus lunatus 

 may be quite free from any furrows as not infrequently happens 

 in Cebus, Macacus and Cercopithecus or only one or two slight 

 grooves may be found. In the majority of all forms however, 

 there is seen a distinct but not deeply incised furrow, extending 

 from the occipital pole upward toward the center of the lunate. 

 It is the external calcarine fissure of Cunningham, sulcus occipi- 

 talis of Retzius, sulcus opercularis of Brodmann. In conformity 

 with the B.N.A. usage it may be called the sulcus calcarinus 

 lateralis. Its length and depth vary although its general direc- 

 tion and location are quite constant. In addition smaller much 

 shallower accessory furrows are frequently present, above or 

 below the lateral calcarine or the latter may be branched. The 

 retrocalcarine sulcus usually ends in a very pronounced verti- 

 cal bifurcation on the mesial surface but occasionally it may re- 

 main unbranched and extend outward upon the occipital pole 

 above or between the branches of the lateral calcarine. 



The sulcus praelunatus, which is the sulcus occipitalis lateralis 

 of Eberstaller, so frequent in the Simiidae, is only slightly or 

 occasionally indicated (cf. Retzius '06, Nasahs larvatus, plate 

 33, Macacus, plates 24 and 27). 



In addition to the above mentioned sulci, small shallow in- 

 constant foldings of the cortex may occur in front of the sulcus 

 lunatus, between it and the superior temporal and to these we 

 shall refer later. 



From the foregoing account it will be evident that the lower 

 Old World forms conform quite closely to a rather simple plan in 



