332 N. W. INGALLS 



also to the commencing development of the parietal area in front. 

 These two factors with their individual variations determine the 

 form, position and relations of the lunate. In Hylobates and even in 

 some of the higher Cercopithecidae, the tide has turned against it 

 and while in Chimpanzee conditions may seem to be more or less 

 in the balance, in Orang and Gorilla the process is still more ad- 

 vanced. The great sulcus, ''Affenspalte" of Cynocephalus, for 

 example, is still represented in man and it is determined and de- 

 fined by the conditions exhibited in the various annectant gyri, not, 

 according to Zuckerkandl as to its homology and morphological 

 value, but solely as regards its form, position and relations. 



The expansion of area 19 below the lateral end of the lunate has 

 led to similar but more far reaching and radical changes in the in- 

 ferior occipital sulcus of lower Primates. Originally, in its pos- 

 terior part, an inferior bounding sulcus, sulcus infrastriatus, it 

 gradually loses this exact significance and with the recession of 

 the striate area it does not, like the lunate, follow it, being pos- 

 sibly prevented mechanically by the interposed end of the lunate, 

 and hence becomes broken up and tends to disappear. In Hylo- 

 bates it is as a rule much reduced and inconstant and its recog- 

 nition in the higher forms and in men, as a sulcus sublunatus, is 

 difficult if not practically impossible. Some of the small grooves 

 behind the lunate and below the lateral calcarine might be in- 

 terpreted as its last remnants. Further observations will be re- 

 quired to determine its exact fate. 



The sulcus referred to above as developing out of the Quer- 

 furche of Zuckerkandl which is commonly encountered in the 

 higher Simiidae and in man, occupies an analogous but in no 

 sense an homologous position in the occipital region. It would 

 seem at first glance to be the inferior occipital of the human brain 

 which forms the lateral limit of the peristriate area, but this sul- 

 cus in man does not represent this limit of the primitive area 19, 

 if we suppose that the paratemporal area, 37, is derived from it 

 since it is located between this area in front and the temporo- 

 occipital behind. It may be that furrows representing the descend- 

 ing branch of the parallel sulcus, which cuts directly into area 19, 

 can be brought into relation with the inferior occipital and that 



