81 



In most humao brains the operculum is less extensive than it is 

 in the example represented in Fig. 1. As the operculum shrinks the 

 line of the lunate sulcus (on the surface) becomes less curved and 

 more nearly horizontal (Fig. 5): in other words it ultimately becomes 

 identical with the direction of the depth of the sulcus lunatus. This 

 destroys to a considerable extent the resemblance to the Simian brain : 

 yet, if the operculum be cut away from a l)rain such as that repesented 

 in Fig. 1 a condition practically identical with that shown in Fig. 5 

 will be produced. There can now be no difficulty concerning the 

 identification of the sulcus lunatus in Fig. 5 with the "sulcus occipitahs 

 lateralis" of Human Anatomy. But I have discarded the latter term 

 because it is applied by many anatomists to the sulcus occ. superior 

 of the Apes: in order to prevent this undesirable confusion between 

 the sulcus lunatus and the sulcus occipitalis superior it seems advisible 

 to discard altogether the term "sulcus occipitalis lateralis". 



S. intraparietalis 



S. i^ar. occ. 



S. intraparietalis 



S. occ. inferior 



occ. trans. 



S. occ. 

 parames. 



_ S. occ 

 lunatus 



^ ' S. occ. superior. 



S. occ. inferior 

 Fig. 5. Fig. 6. 



Figs. 5 and G. The lateral aspect of the left occipital region in two Egyptian 



S. occ. 

 parames. 



S. occ. superior 



brains. Ad naturam del. ^4 i^^t. size. 



The sulcus lunatus (in the form usually called "lateralis") is a 

 fairly constant feature of the human brain: in other words, the „Affen- 

 spalte", far from being a distinctive feature of the Apes, is a normal 

 sulcus in the human brain. This statement is widely opposed to the 

 views of most writers. Thus Cunningham describes and figures the 



Anat. Anz. Aufsätze. XXIV. 



