THE CEREBRUM. 539 



6. The para-central fissure begins at the supero-mesial border of the hemis- 



phere. It then passes downward and forward for a variable distance 

 and then turns upward enveloping a lobule known as the para- 

 central lobule. 



7. The super-callosal fissure extends from a point just anterior to the para- 



central lobule downward and forward below the rostrum of the corpus 

 callosum. 



Secondary fissures of more or less importance are present in the different 

 lobes, subdividing the surface into convolutions: e.g., in the frontal lobe are 

 found the pre-central, the super-frontal, medi-frontal and sub-frontal fissures; 

 in the temporal lobe the super -temporal and medi-temporal fissures. 



Convolutions. The convolutions or gyri are the portions of the cere- 

 bral surface comprised between the fissures. The arrangement of the sur- 

 face 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 

 super-, medi-, and sub-frontal convolutions. 



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



the Rolandic or central fissure, with which it corresponds in direction. 

 It is continuous above with the super-frontal and below with the sub- 

 frontal convolution. 



2. The super-frontal convolution or gyrus is bounded internally by the longi- 



tudinal fissure and externally by the super-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 medi-frontal convolution or gyrus is situated on the side of the lobe, 



between the super-frontal fissure above and the medi-frontal fissure 

 below. Its general direction is downward and forward. 



4. The sub-frontal convolution or gyrus winds around the pre-sylvian branch 



of the fissure of Sylvius in the anterior and inferior portion of the frontal 

 lobe. 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 super- 

 and sub-parietal. The latter is again subdivided into the marginal and the 

 angular convolution. 



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



Rolandic or central fissure, with which it corresponds in direction. 

 Above, it is continuous with the super-parietal convolution; below, with 

 the marginal and the pre-central convolutions. 



2. The super -parietal convolution or gyrus is bounded internally by the longi- 



tudinal 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. 



