384 NERVOUS SYSTEM. 



the adjacent surface of the brain. These several branches of 

 the arteria anterior reach as far as the upper convex surface of 

 the brain, and there anastomose with other arteries. 



The Internal Carotid may now be considered to have lost its 

 name, and the trunk is continued as Arteria Media Cerebri. It 

 is directed outwards, and engages in the fissure of Sylvius; 

 while there it detaches a great number of branches to the ad- 

 joining surfaces of the anterior and of the middle lobe. Some 

 of these branches are of considerable magnitude, and winding 

 along the convolutions of the brain, they at length ascend to the 

 upper surface of the hemisphere, arid anastomose with the 

 branches of the anterior and of the posterior cerebral artery. 



The Vertebral Artery (Arteria Vertebralis) is a branch of the 

 subclavian. In order to reach the cavity of the cranium it 

 has to traverse the foramina of the transverse processes of the 

 six upper vertebrae of the neck. It ascends in a straight line 

 till it reaches the second vertebra, but there, in order to pass 

 through the transverse process, it takes a direction upwards 

 and outwards. It then ascends vertically again till it has 

 passed through the transverse process of the first vertebra. 

 After which it takes a horizontal course, winding around the 

 posterior face of the upper oblique process of the same verte- 

 bra, in a depression for the purpose, and having reached the 

 internal extremity of this process, it ascends upwards and in- 

 wards through the occipital foramen into the cavity of the cra- 

 nium, perforating the dura mater just above the condyle of the 

 occipital bone. Having got into the cranium, it is first on the 

 side and then on the under surface of the medulla oblongata, 

 and continues to approach its fellow till it reaches the posterior 

 margin of the tuber annulare. At this point the two verte- 

 bral arteries coalesce, and from their union results the basilar 

 artery. 



The vertebral artery in this course, from its origin to its ter- 

 mination, detaches several arterioles to the heads of the adjoin- 

 ing muscles, to the membranes of the spinal marrow, and to the 

 nerves as they come out of the interverlebral foramina : they 

 are generally too small and irregular (o deserve a special de- 

 scription. At its upper extremity, however, it sends off three 



