443 



parallel to the hippocampal fissure, from which it is separated by the 

 gyrus fornicatus: into the latter the so-called "fissura calcarina" — the 

 superficial cleft formed by the meeting of the two lips of the fossa 

 striata — appears to cut deeply in the undisturbed hemisphere. 



The lower lip of the fossa striata in Cercopithecus (and many 

 other Apes) is often indented by a shallow furrow, which is a sulcus 

 Umitans inferior areae striatae (Fig. 7). This furrow is not visible 

 until the hps are drawn apart. 



The posterior end of the fossa striata bends downward and forms 

 the lower limb of the apparently bifid caudal extremity. The upper 

 limb (s. i. m. ]r. d.^) is formed as a kink in the dorsal lip or as a cleft 

 between the posterior end of the opercular upper lip and the large 

 depressed caudal part of the area striata (Fig. 7). In those brains 

 (e. g. Seranopithecus) in which the upper lip of the fossa striata is 

 not operculated the posterior end of the fossa striata is not bifid. In 

 Semnopithecus there is a very large lower operculum, which overlaps 

 the deeper wall of the fossa, and no upper operculum: the posterior 

 part of the area striata (in that genus) usually becomes exposed on 

 the surface (of what most writers call the "cuneus") and a sulcus limi- 

 tans superior areae striatae makes its appearance. I'his may also 

 happen in some cases in Hylobates and the other Anthropoid Apes. 



In the human brain a vertical section through any part of the 

 posterior half of the area striata presents a very different appearance 

 (Fig. 8) to that of the corresponding section in an Apes' brain (Fig, 5). 

 The whole of the area is not folded inward as it is in Cercopithecus: 

 a comparatively shallow axial furrow has developed (s. *. m) — a sulcus 

 intrastriatus, as we may call it — and a considerable part of the area 

 striata is not involved in its formation, but lies on the surface forming 

 part of the cuneus and lingual gyrus. In most cases definite limiting 

 furrows — the superior in the cuneus, and the inferior in the lingual 

 gyrus — are developed opposite the edges of the stria Gennari. Al- 

 though both the fossa striata of the Apes and the sulcus intrastriatus 

 of Man are formed by the involution of the area striata they are not 

 strictly homologous, because the former consists of a folding of the 

 whole area, whereas the latter is a mere pucker in its surface. The 

 depth and position of the intrastriate sulcus (or sulci, for it is often 

 represented by several furrows) are subject to a very wide range of 

 variation in the human brain. It is the furrow which in previous 

 works I have called "sulcus retrocalcarinus". It may consist of one 

 simple furrow in the axis of the area striata or it may consist of 

 several furrows separated by gyri (exposed or submerged). Its caudal 



