VEKTEBEAL AETEEY. 905 



(9) Arteria Cerebri Media. The middle cerebral artery is the larger of the 

 two terminal branches, and the more direct continuation of the internal carotid 

 artery. It passes laterally, in the stem of the lateral fissure (Sylvius), to the 

 surface of the insula, and it divides, in the posterior part of the circular sulcus 

 (Eeil), into parieto-temporal and temporal terminal branches. 



Branches. (a) The central or basal, which constitute the antero- lateral basal 

 arteries, are numerous and very variable in size. They arise at the base of the brain, 

 in the region of the anterior perforated substance. Two sets, known as the medial and 

 the lateral striate arteries, are distinguishable. 



(a 1 ) The medial striate arteries pass upwards through the two medial segments 

 of the lentiform nucleus (globus pallidus) and the internal capsule to terminate in the 

 caudate nucleus. They supply the anterior portions of the lentiform and caudate nuclei 

 and of the internal capsule. 



(a 2 ) The lateral striate arteries pass upwards through the lateral segment (puta- 

 men) of the lentiform nucleus, or between it and the external capsule, and they form two 

 sets : an anterior, the lenticulo-striate, and a posterior, the lenticulo-optic ; both sets 

 traverse the lentiform nucleus and the internal capsule, but the lenticulo-striate arteries 

 terminate in the caudate nucleus, and the lenticulo-optic in the thalamus. One of the 

 lenticulo-striate arteries, which passes in the first instance round the lateral side of the 

 lentiform nucleus, and afterwards through its substance, is larger than its companions ; it 

 frequently ruptures, and is known as the " artery of cerebral haemorrhage." 



(b) Cortical branches are given off as the middle cerebral artery passes over the surface 

 of the insula at the bottom of the lateral fissure, as follows : 



(6 1 ) The lateral orbital runs forwards and laterally, and is distributed to the 

 lateral part of the orbital surface of the frontal lobe and to the inferior frontal gyrus. 



(b 2 ) The inferior lateral frontal, which supplies the inferior and middle frontal 



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(6 3 ) The ascending frontal, which turns round the upper margin of the lateral fissure, 

 and is distributed to the anterior central gyrus and to the posterior part of the middle 

 frontal gyrus. 



(6 4 ) The ascending parietal branch emerges from the lateral fissure (Sylvius) and 

 passes upwards along the posterior border of the posterior central gyrus, supplying that 

 gyrus and the superior parietal lobule. 



(6 5 ) The temporal branch passes out of the lateral fissure, and turns downwards to 

 supply the superior and middle temporal gyri. 



(6 6 ) The parieto-temporal branch continues backwards, in the direction of the main 

 stem of the middle cerebral artery, and emerges from the posterior end of the lateral 

 fissure ; it supplies the inferior parietal lobule, part of the lateral surface of the occipital 

 lobe, and the posterior part of the temporal lobe. 



ARTERIA VERTEBRALIS. 



The vertebral artery (Figs. 757 and 761) is the first branch given off from 

 the subclavian trunk; it arises from the upper and posterior part of the parent 

 stem, opposite the interval between the anterior scalene and the longus colli 

 muscles, and terminates at the lower border of the pons (Varolii) by uniting with 

 its fellow of the opposite side to form the basilar artery. 



Course and Relations. The vertebral artery is divisible into four parts. 



The first part runs upwards and backwards, between the scalenus anterior and 

 the lateral border of the longus colli, to the foramen in the transverse process of the 

 sixth cervical vertebra. It is surrounded by a plexus of sympathetic nerve fibres, 

 is covered anteriorly by the vertebral and internal jugular veins, and it may be 

 crossed anteriorly by the inferior thyreoid artery. On the left side the terminal 

 ; part of the thoracic duct also passes anterior to it. The second part runs upwards 

 through the foramina in the transverse processes of the upper six cervical vertebrae. 



far as the second cervical vertebra its course is almost vertical ; as it passes 

 through the transverse process of the epistropheus, however, it is directed obliquely 

 upwards and laterally to the atlas. It is surrounded by a plexus of sympathetic 

 nerve fibres, and also by a plexus of veins. The artery lies anterior to the trunks 

 of the cervical nerves, and medial to the intertransverse muscles. The third part 



