THE BASILAR ARTERY". 267 



has a lateral and external aspect. After passing the transverse 

 process of the Atlas, it is turned suddenly backwards, in a 

 groove, and finally passes through the great occipital foramen 

 into the cavity of the cranium. It then proceeds upon the 

 cuneiform process of the occipital bone, under the Medulla 

 Oblongata, and joins its fellow so as to form an acute angle 

 with it near the union of the medulla oblongata with the pons 

 Varolii. From each of the vertebral arteries before their 

 union, there generally goes off a small branch called the Pos- 

 terior Meningeal, which is spent upon the posterior part of the 

 dura mater. 



The trunk formed by the union of the vertebral arteries is 

 called 



The Basilar Artery. 



It extends forward near to the anterior part of the pons 

 Varolii, where it bifurcates ; but previously sends off several 

 branches on each side. The first pair go off in a lateral 

 direction, soon after its commencement, near the back part of 

 the pons Varolii, and are spent upon the medulla oblongata, 

 the pons Varolii, and the other contiguous parts, and also upon 

 the fourth ventricle and the Plexus Choroides of that cavity. 

 They are called the Posterior or Inferior Arteries of the Cere- 

 bellum. 



Two other lateral branches, which are called the Superior 

 Arteries of the Cerebellum, go off from the Basilar artery, 

 near its anterior extremity. These are principally spent upon 

 the crura of the cerebellum and cerebrum : upon the cerebel- 

 lum itself, and the contiguous parts. 



Soon after sending off the last mentioned arteries, the Basi- 

 lar artery divides into two branches, which also take a lateral 

 direction, and are of considerable size. In their course out- 

 ward, these branches are curved with their convexity forward. 

 About ten or twelve lines from its commencement, each of 

 them sends off a branch called the Arteria Communicans, 

 which passes directly forward, and communicates with the 

 internal carotid, thus forming the arrangement which is called 



