THE FOEM-EELATIONS OF THE HUMAN BEAIN. 



195 



ascends toward the edge of the hemisphere and thus considerably interrupts 

 the continuity. 



This branchj the fissura retrocentralis superior, often occurs independent of 

 the interparietal fissure. The interparietal fissure allows the recognition of three 

 divisions, which are occasionally separate from one another. The anterior division is 

 called the fissura retrocentralis inferior, the posterior the sulcus occipitalis amte- 

 terior or perpendicularis. 



The portion of the inferior parietal lobule which surrounds the end of 

 the fissure of Sylviiis is called the gyrus marginalis. The part that lies just 

 back of this and arches around the superior temporal sulcus is the gyrus 



Fig. 131. — Lateral aspect of brain. 



angularis. The former gyrus is at once observed on every brain; the latter 

 must be searched for with some diligence. It is found in the space bounded 

 above by the interparietal fissure and below by the superior temporal sulcus; 

 that is to say, its end. Its posterior part, indeed, just surrounds the end of 

 this sulcus. The region of the gyrus angularis is an important one, and it 

 is therefore advantageous to be able to locate and bound it well. The small 

 gyrus directly posterior to it is the gyrus parietalis posterior. 



The occipital lohe is not so uniformly fissured in all brains that the 

 convolutions described by writers as superior, middle, and inferior may be 

 easily identified without elaboration. It is commonly separated from the 

 parietal lobe by the anterior occipital sulcus, which passes vertically down- 



