THE CEREBRAL ARTERIES 119 



the lateral wall of the cavernous sinus, lying between the 

 endoperiosteum and the endothelial lining. At the anterior 

 clinoid process (Fig. 58) it pierces the dura mater and, 

 opposite the anterior perforated substance (spot), it ends by 

 dividing into the anterior and middle cerebral arteries. 



The Middle Cerebral Artery inclines laterally across the 

 anterior perforated substance and enters the lateral fissure (of 

 Sylvius). It then courses over the surface of the island (of 

 Reil) and extends backwards in the posterior ramus of the 

 lateral fissure. It gives off a number of cortical branches^ 

 which emerge from the fissure and supply the whole of the 

 lateral surface of the hemisphere, with the exception of a strip 

 along its superior and inferior margins. Further, they do not 

 supply the occipital lobe. The middle cerebral artery, there- 

 fore, supplies (i) The whole of the motor area, except the lower 

 limb centres; (2) the motor speech centre; (3) the centre for 

 written speech; (4) the word-hearing centre; and (5) the 

 word-seeing centre (Fig. 3). 



As it crosses the anterior perforated substance, the middle 

 cerebral artery gives off several central branches, which at once 

 pass upwards and enter the brain. They thus come into 

 relationship with the lentiform nucleus (p. 33) and they 

 ascend across its lateral surface for a short distance before 

 they pass medially into its substance. The lenticulo striate 

 arteries traverse the anterior part of the lentiform nucleus and 

 the anterior limb of the internal capsule and terminate in the 

 head of the caudate nucleus. The lenticulo-optic arteries are 

 placed more posteriorly, and consequently pass through the 

 posterior limb of the internal capsule before they reach the 

 thalamus. The artery of cerebral haemorrhage belongs to 

 the former group. 



The central arteries, as they lie in the brain substance, are 

 poorly supported and they are, in consequence, frequently 

 the site of small aneurismal dilatations. When small emboli 

 are carried into the middle cerebral artery, they are usually 

 arrested in the cortical branches and only rarely enter the 



