NERVOUS SYSTEM. VEItTEBRATA. 1 I . r > 



joined to the Sylvian sulcus, it is worthy of note that it is 

 absent, at any rate as a separate element, in all the .-i^ht 

 hemispheres of the Gorilla. There is a small diagonal 

 sulcus of Eberstaller on both hemispheres, and tin- low.-r 

 end of the central (Rolando's) sulcus is curved forward 

 into such a position that it would relieve the tension of tin- 

 expanding cortex which expends itself in the Orang in the 

 formation of the inferior transverse sulcus. 



The parallel sulcus is prolonged into a very extensive 

 hook around the end of the Sylvian fissure on the left 

 hemisphere. On the right hemisphere the recurved portion 

 of the '' hook " is a separate triradiate sulcus. The drop, 

 richly-branched intraparietal sulcus extends around thcsr 

 sulci. Its lower extemity is linked (superficially) to tin- 

 Sylvian fissure by a deep, oblique sulcus, the free end of 

 tthich extends towards and seems to accentuate the bend in 

 the central sulcus. The very irregular and unsyminetrical 

 ramus postcentralis superior is not joined to the intra- 

 parietal ; but the latter gives off deep branches (two on the 

 right and one on the left side) alongside the chief element 

 of the ramus. Posteriorly the intraparietal sulcus dip> 

 into the Simian sulcus (Affenspalte) and is hidden unl r 

 the occipital operculum. The apparent bifid mesial ex- 

 tremity of the Affenspalte may represent the transverse 

 occipital sulcus. 



The arcus occipitalis is very large and wholly exposed, 

 the mesial end of the occipital operculum having been 

 pushed completely outward and backward. 



There is a typical, obliquely placed, Y-shaped lateral 

 occipital sulcus in all eight hemispheres. 



The occipital operculum is bounded by an almost hemi- 

 spherical Affenspalte, both the superior (mesial) and 

 inferior (lateral) extremities of which are about 1 cm. 

 distant from the dorso-mesial and tentorial borders 

 respectively. 



The calcarine sulcus (of the left hemisherc, in which 

 alone it is wholly exposed) is an unbranched furrow of 

 which the anterior half (calcarine sensu stricto) is much 

 deeper than the posterior half (retrocalcarine). Tin- caudal 

 extremity of the latter bends almost at right angle* an.l 



