1344 



A MANUAL OF ANATOMY 



two posterior cerebral arteries is effected by means of the basilar 

 artery ; the connection between the posterior cerebral and internal 

 carotid arteries is effected by means of the posterior communicating 

 artery ; and the connection between the two anterior cerebral 

 arteries is effected by means of the anterior communicating artery. 

 These communications serve to insure a regular supply of arterial 

 blood to the brain in cases of obstruction to one or other of the 



Great Longitudinal 

 Fissure 



Inferior Frontal 

 Gyrus 



Sulcus Occipitalis 

 Lateralis 



Sulcus Occipitalis'' "%^' / 

 Sulcus Occipitalis Transversus' 



I 



External Parieto-occipital Fissure 



Fig. 561. — The Cerebral Hemispheres (Superior View). 



principal arterial trunks. The communications also serve to equalize 

 the circulation of blood through the different parts of the brain. 



Superior Surface of the Brain. — ^The brain is ovoid superiorly, its 

 greatest breadth corresponding to the positions of the parietal 

 eminences of the parietal bones. In the median line it presents 

 a deep cleft, called the great longitudinal fissure, which extends from 

 the front to the back, and divides it into two hemispheres, right 

 and left. This fissure is occupied by a process of the dura mater, 

 called the falx cerebri, and the corpus callosum lies at its deep part. 

 In front of the corpus callosum the fissure extends down to, and is 



