THE NERVE SYSTEM 



3. The dorsal or opercular surface of the temporal lobe enters into the formation 

 of the sylvian cleft. It is but slightly marked by a few oblique or transverse 

 furrows (transtemporal fissures) demarcating slightly elevated transtemporal gyres. 



GYRES OF THE TEMPORAL LOBE. The five principal fissures named subdivide 

 the lobe into five gyres. On the lateral surface lie the supertemporal, meditemporal, 

 and subtemporal gyres (gg. temporalis superior, media* cf inferior); on the ten- 

 torial surface are the subcalcarine (gyrus lingualis), subcollateral (gyrus fusiform.!*; 

 g. occipitotemporalis) and part of the subtemporal. 



The hippocampal gyre (gyrus hippocampi), formerly included in the " limbic 

 lobe," but morphologically belonging to the neopallium, occupies the dorsimesal 

 part of the ventral surface of the temporal lobe. The longer or shorter extension 

 of the occipitocalcarine stem partially (forming the isthmus gyri hippocampi) 

 interrupts its continuity with the callosal gyre. It is demarcated by the collateral 

 fissure (in part) and the hippocampal fissure, broadens out toward the temporal 

 pole, and appears to become bent upon itself dorsally to form the uncinate gyre 

 (uncus). As will be learned in the sequel, the hippocampal gyre is demarcated 

 from the uncus proper by the intervention of the frenulum Giacomini an exten- 

 sion of the narrow, gray, dentate gyre. 



OLFACTORY 

 LOBE 



FIG. 677. Brain of a six-months' human embryo, FIG. 678.- Cerebrum of an eight-months' human embryo, 

 natural size, right side. (Kolliker.) leftside. The insula is nearly covered in. (Testut.) 



Near the temporal pole it is demarcated from the subcollateral gyre by the 

 fissura rhinica, 1 or postrhinal fissure; this fissure is not infrequently confluent with 

 the collateral. 



The surface of the hippocampal gyre, particularly in the zone along the hippo- 

 campal fissure, is of a more whitish color than is characteristic of other cerebral 

 gyres; this is due to a white reticular stratum of fibres, the substantia reticularis alba 

 (Arnold). The convex, broader part of the gyre is marked by numerous small, 

 wart-like eminences, resembling the skin of an amphibian, and called by Retzius 

 the verrucae gyri hippocampi. Just ventrad of the uncinate portion, or the ter- 

 minus of the hippocampal fissure, lies a groove marking the impression of the 

 free edge of the tentorium cerebelli. 



The Island of Reil (central lobe or insula) (Figs. 678, 679). The island of Reil 

 lies deeply in the sylvian cleft and can only be seen when the lips of that cleft are 

 widely separated, since it is overlapped by the opercula already described. With 

 the opercula removed, the island of Reil presents a tetrahedral shape with its apex 

 or pole directed ventrocephalad. Its borders are sharply outlined by the cir- 

 cuminsular fissure except in the depths of the basisylvian cleft, where the insular 

 cortex is continuous with the gray substance of the anterior perforated substance 



1 Called by Wilder, on account of its correlation with the amygdaline nucleus, the amygdalinc fissure. Schwalbe 

 calls it (in part) the inrisara temporalis. 



