FISSURES AND SULCI OF CONVEX SURFACE. 5$ 



cleft between the hemispheres of the cerebrum (Figs. 19 and 22). 

 It contains the falx cerebri (Fig. i). Its floor is formed by the 

 corpus callosum. The cerebrum is separated from the cere- 

 bellum by the transverse fissure of the cerebrum (fissura 

 transfer sa cerebri, Figs. 20, 27, i and 6). This fissure continues 

 forward above the mid-brain, and terminates in the cerebrum 

 between the inter-brain and the fornix, where it is continuous, 

 by its lateral extremities, with the chorioidal fissures of the hem- 

 ispheres. The tentorium occupies the posterior part. The 

 anterior part of the transverse fissure contains the chorioid tela 

 of the third ventricle. 



There are three great furrows in the convex surface of each 

 cerebral hemisphere which form interlobar boundaries and con- 

 stitute very important landmarks: The fissura cerebri lateralis, 

 the sulcus centralis, and the sulcus occipito-parietalis (Figs. 22 

 and 23). 



The lateral fissure (fissura cerebri lateralis, [Sylvii]) begins 

 in the fossa of the same name at the base of the brain (Fig. 21). 

 It runs outward between the frontal and the temporal lobe, along 

 the lesser wing of the sphenoid bone ; and, turning upward, on the 

 convex surface, it divides three- fourth inch behind the Sylvian point 

 into an anterior horizontal, and anterior ascending and a posterior 

 ramus (Fig. 23). Into the frontal lobe project the small anterior 

 rami. They are separated by the foot (posterior end) of the inferior 

 frontal gyrus, called the pars triangularis. Below the anterior 

 horizontal ramus is a knuckle of the same frontal gyrus which 

 forms the pars orbitalis; and, between the ascending and posterior 

 rami, is located the pars opercularis, constituting the connecting 

 gyrus between the anterior and posterior central gyri. The 

 inferior frontal gyrus forms the frontal part of the operculum 

 (pars frontalis operculi). The operculum (operculum, a cover) 

 covers the island. The posterior limb of the lateral cerebral 

 fissure separates the temporal lobe from the parietal. Near 

 the crotch and within the fissure is situated the island. A line 

 drawn from the Sylvian point, one and one-quarter inches be- 

 hind the zygomatic process of the frontal bone and one and a half 

 inches above that of the temporal, backward to the subparietal 



