450 THE BRAIN 



soon breaks up into a number of large terminal branches, 

 which spread out on the surface of the insula. Before the 

 posterior ramus of the lateral fissure is opened up, to expose 

 the insula, these branches may be seen emerging from between 

 its two lips (Fig. 1 80). Then they diverge and supply a 

 wide area of cortex on the lateral surface of the hemisphere. 



The branches which spring from the middle cerebral artery may be 

 classified as follows : 



Ante ro ,a,e ra ,. 



f Lateral orbital. 

 Frontal -! Inferior lateral frontal. 



( Ascending frontal. 

 Cortical branches, j Parietal { Ascending parietal< 



Parieto-temporal. 

 Temporal. 



The arteries of the ant ero -lateral basal group are very numerous. They 

 pierce the substantia perforata anterior and supply the lentiform nucleus, 

 the internal and the external capsule, the caudate nucleus, and a portion of 

 the thalamus. 



The frontal and parietal branches turn round the upper lip of the 

 posterior ramus of the lateral fissure and ascend on the lateral surface of the 

 hemisphere. The frontal branches are: (i) lateral orbital to the lateral 

 part of the orbital surface of the frontal lobe ; (2) inferior lateral frontal 

 to the inferior and middle frontal gyri ; (3) ascending frontal ', which runs 

 upwards in relation to the anterior central gyrus. 



The ascending parietal branch extends in an upward and posterior 

 direction in relation to the postcentral gyrus, and its terminal twigs supply 

 the greater part of the cortex of the superior parietal lobule. 



The parieto-temporal branch is a very large artery which issues from 

 the posterior part of the posterior branch of the lateral fissure ; it sends 

 branches upwards to the inferior parietal lobule, and others which incline 

 downwards over the posterior part of the temporal lobe. Its twigs, as 

 a rule, do not encroach upon the lateral surface of the occipital lobe. 



The temporal branches, two or three in number, issue from the posterior 

 ramus of the lateral fissure, and, turning downwards and posteriorly, over 

 its lower lip (i.e. the superior temporal gyrus), they ramify upon the 

 lateral surface of the temporal lobe. 



Circulus Arteriosus (O.T. Circle of Willis). This re- 

 markable anastomosis is placed beneath the base of the brain 

 in the deep hollow anterior to the pons. It takes the form 

 of a heptagonal or hexagonal figure, and the vessels which 

 compose it lie in the cisterna interpeduncularis and the cisterna 

 chiasmatis. Anteriorly it is closed by the anterior communi- 

 cating artery which links together the two anterior cerebral 

 arteries. On either side is the posterior communicating 

 artery connecting the internal carotid (from which the anterior 



