THE CEREBRAL ARTERIES 



563 



enter the posterior perforated substance and supply the medial portion of the optic thalamus, 

 and the walls of the third ventricle; the posterior chorioid pass through the transverse fissure 

 to the tela chorioidea (velum interpositum) and chorioid plexus; the postero -lateral run to 

 the posterior part of the optic thalamus and give branches to the cerebral peduncles and the 

 corpora quadrigemina. 



The cortical branches of the posterior cerebral supply the entire occipital lobe and all of the 

 temporal lobe except the superior temporal gyrus (fig. 459). 



In regard to the cerebral arteries in general it may be said that there is no anastomosis 

 between the cortical and central branches, the two forming distinct and separate systems. 

 The cortical may or may not anastomose with each other, but the communication between the 

 neighbouring cortical branches is seldom sufficient to maintain the nutrition of an area when 

 the vessel that normally suppUes it is obstructed. The central branches are so-called end- 

 vessels and do not anastomose with each other. Hence obstruction of the middle cerebral 

 artery leads to softening of the area supphed by its central branches, but not always to softening 

 of the region supphed by its cortical branches. Indeed, the cortical region may escape com- 

 pletely, although the central area is irreparably disorganised. The gross anastomosis of the 

 posterior cerebral with the anterior cerebral arteries through the circulus arteriosus has already 

 been described. To sum up the distribution of the cerebral arteries, the branches of each are 

 divided into the central, or ganglionic and the peripheral or cortical. The central branches 

 arise at the commencement of the cerebral arteries about the circulus arteriosus whilst the 

 cortical are derived chiefly from the termination of these vessels. 



Fig. 460. — The Arteries of the Lateral Surface op the Brain. (After Toldt, 

 Human Anatomy," Rebman, London and New York.) 

 Central sulcus (Rolandi) 



■ Atlas of 



Branches of the anterior cerebral artery 



Branches of the posterior 



cerebral artery 



Branches of the anterior cere- 

 bral artery 



Optic nerve 



Middle cerebral artery 



Branch of the posterior cerebral 

 artery 



(A) The central branches are divided into four sets— two median and two lateral. 1. 

 The two median are — (1) The antero -median, which arise from the anterior cerebral and the 

 anterior communicating, and supply the fore end of the caudate nucleus, and (2) the postero- 

 median, which arise from the posterior cerebral and supply the medial part of the optic thalamus 

 and neighbouring wall of the third ventricle. 2. The two lateral are: — (1) The antero -lateral 

 arise from the middle cerebral, and, passing through the anterior perforated substance, supply 

 the lenticular nucleus, the posterior part of the caudate nucleus, the internal and external 

 capsules, and the lateral part of the optic thalamus. (2) The postero-lateral arise from the 

 posterior cerebral, and supply the hinder part of the optic thalamus, the pedunculus cerebri, and 

 the corpora quadrigemina. 



(B) The cortical branches ramify in the pia mater, giving off branches to the cortical 

 substance, some of which extend through it to the underlying white substance. 



It will be seen that the middle cerebral supphes the somsesthetic area of the cortex. It 

 also supphes the cortical auditory centre, and, in part, the higher visual centre. The anterior 

 cerebral supphes only a small part of the somsesthetic area, namely, the part of the leg centre 

 that occupies the paracentral lobule and the highest part of the anterior central gyrus. The 

 posterior cerebral supphes the visual path from the middle of the tract backward, and the half 

 vision centre in the occipital lobe. It supphes also the corpora quadrigemina and the sensory 

 part of the internal capsule. 



The branches which supply the cerebellum and brain stem are given in connection with 

 the vertebrals on page 561. 



