212 DISSECTION OF THE DOG 



the length of the hemisphere ; i.e. the corpus callosum does not reach the 

 frontal and occipital poles of the hemisphere. 



The surface of the hemisphere is sculptured by lines, known as fissures 

 (fissurffi) and sulci, which separate winding ridges referred to generally as 

 convolutions (gyri). 



Lateral surface.— A fissure of great fundamental importance— the rhimil 

 fissure (fissura rhinaUs)— separates the olfactory and pyriform lobes from 

 the rest of the lateral surface. That part which is dorsal to the rhinal fissure 

 is covered with convolutions, rising tier above tier, and arranged in a curved 

 manner about a short straight fissure of considerable depth, the lateral cerebral 

 fisstire of Sylvius (fissura cerebri lateralis [Sylvii]). The Sylvian fissure occurs 



s. cTiictalns 



s. suprasylvius 



s. ecipsylvius 



s. eciiilateralis 



posUateralis 



TTactus olfactorius 



's, postsijlvius 



Fissura cerebri 

 lateralis [Sylvii] 



Fig. 65. — Lateral surface of the cerebral hemisphere. 



on a level with that transverse depression which crosses the pyriform lobe. 

 In the depths of the fissure, and in the natural condition hidden from sight, 

 are several short convolutions composing the insula. 



Bent round the Sylvian fissure is a convolution bounded on the other 

 side by a sharply curved ectosylvian sulcus (sulcus ectosylvius) . More dorsal 

 in position is a sulcus comprised in reahty of two parts, though in the majority 

 of specimens its double character is not apparent. The oral segment is one 

 of the deepest of the several cerebral sulci, and is known as the swprasylvian 

 sulcus (s. suprasylvius) . Continuous with this, and united to it at an angle, 

 is the post-sylvian sulcus (h. postsylvius). The area between the suprasylvian 

 sulcus and the dorsal margin of the hemisphere is cut by the lateral sulcus 

 (s. lateralis) generally, but not always, continuous anteriorly with the coronal 

 sulcus (s. coronalis). The coronal can be distinguished from the lateral sulcus 

 by its greater distance from the margin of the hemisphere. Small sulci of 



