CEREBRUM. 489 



ment of the surface is such that only the more superficial portions are 

 visible. The depth of the convolution, the portion bordering the 

 fissure, is concealed from view. Each lobe presents a series of such 

 convolutions, which differ considerably in their relative physiologic 

 importance. 



The Frontal Lobe. The frontal lobe presents on its convex 

 surface four convolutions : viz., the anterior or pre-central convolution, 

 and the superior, middle, and inferior frontal convolutions. 



1. The anterior or pre-central convolution is situated just in front of 



the Rolandic or central fissure, with which it corresponds in 

 direction. It is continuous above with the superior frontal and 

 below with the inferior frontal convolution. 



2. The superior frontal convolution is bounded internally by the 



longitudinal fissure and externally by the superior frontal fissure. 

 From the upper end of the pre-central convolution, with which 

 it is continuous, it runs forward and downward to the anterior 

 extremity of the frontal lobe, where it turns backward and rests 

 on the orbital plate of the frontal bone. 



3. The middle frontal convolution is situated on the side of the lobe, 



between the superior frontal fissure above and the middle frontal 

 fissure below. Its general direction is downward and forward. 



4. The inferior frontal convolution winds around the ascending 



branch of the fissure of Sylvius in the anterior and inferior por- 

 tion of the cerebrum. It is continuous posteriorly with the 

 lower end of the pre-central convolution. 



The Parietal Lobe. The parietal lobe presents three well- 

 marked convolutions: viz., the posterior or post-central convolution, 

 and the superior and inferior parietal. 



1. The posterior or post- central convolution is situated just behind 



the Rolandic or central fissure, with which it corresponds in 

 direction. Above, it is continuous with the superior parietal 

 convolution; below, with the inferior parietal and the pre-central 

 convolutions. 



2. The superior parietal convolution is bounded internally by the 



longitudinal fissure and externally by the intra-parietal fissure. 

 From the upper end of the post-central convolution, with which 

 it is connected, it runs downward and backward as far as the 

 parieto-occipital fissure. 



3. The inferior parietal convolution is connected anteriorly with the 



post-central convolution. Passing backward, it winds around 

 the superior extremity of the fissure of Sylvius, in which situa- 

 tion it is known as the supra-marginal convolution. Beyond 

 this point it divides into two portions, one of which runs forward 

 into the temporal lobe above the first temporal fissure, while 

 the other runs downward and backward, following the intra- 



