ARTERIES OF THE BRAIN. 383 



sure of Sylvius. While in the carotid canal, it gives a small 

 branch to the tympanum of the ear, and as it lies on the side of 

 the sella turcica it gives off the anterior and the posterior arte- 

 ry of the cavernous sinus. When it reaches the anterior>li- 

 noid process it sends off a large branch, through the optic fora- 

 men, to the parts contained within the orbit of the eye. This 

 branch is the ophthalmic artery, and what remains of the inter- 

 nal carotid is then distributed to the brain after the following 

 order: 



There are, first of all, some small branches sent to the adja- 

 cent parts; as the pituitary gland, the infundibulum, and the 

 lower part of the third ventricle. 



The Arteria Communicans Posterior is directed backwards 

 and inwards, and runs into the corresponding trunk of the basi- 

 lar artery, called the posterior cerebral. There are some varie- 

 ties in regard to the size and precise point of origin of this trunk, 

 which it would be needless to mention particularly. Besides 

 the important anastomosis formed by it, it detaches several ra- 

 muscles to the adjacent parts of the pia mater. 



The Arteria Choroidea is the next branch from the internal 

 carotid. It goes outwards and backwards, and after detaching 

 some minor branches, it penetrates into the inferior cornu of the 

 lateral ventricle, by the side of the Pons Varolii, and expends 

 itself in ramifications upon the plexus choroides. 



The Arteria Callosa, or Anterior Cerebri, is detached from 

 the internal carotid, opposite the last. It advances in front of 

 the union of the optic nerves, converging rapidly at the same 

 time towards its fellow. Just before the chiasm of the optic 

 nerves, a transverse branch passes between it and its fellow. 

 This branch, the Arteria Communicans Anterior, is of variable 

 length and size in different subjects, being sometimes a line, and 

 on other occasions three or four lines long. 



The arteria callosa then keeps near its fellow on the under 

 surface of the hemisphere, giving out small branches; and having 

 got on a line with the anterior margin of the corpus callosum, it 

 ascends on the flat side of the hemisphere, and divides into an- 

 terior and into posterior twigs. The former supply the fore 

 flat part of the hemisphere; the latter, the corpus callosum and 



