CIRCULATORY SYSTERI. 195 



from the opposite division, thereby forming a vessel nearly equal 

 in size to the internal carotid itself, named the arteria corporis 

 callosi : this is reflected upward and forward around the corpus 

 callosum, and pursues through its entire length the tract of the 

 raphe, detaching as it proceeds numerous lateral twigs for the 

 supply of the corpus. The anterior cerebral artery now subdivides 

 into several branches, which, with the exception of one, are dis- 

 tributed over the anterior lobes of the brain. This one. 



The ophthalmic artery, leaves the cranium through the foramen 

 lacerum orbitale, in company with the nerve of the same name, 

 and at the bottom of the orbit, after forming some anastomoses 

 with the orbital artery, furnishes a twig to the lachrymal gland, 

 long ciliary arteries to the choroid coat and iris, and the central 

 artery to the retina. 



3 and 4. The middle arteries of the cerebrum. 

 These vessels come off directly opposite to each other at right 

 angles from the trunk, take a flexuous passage between the 

 anterior and middle lobes, and ramify extensively within their 

 substance. 



5. The internal artery of the cerebrum; which 

 arises a little higher than the former, pursues the course of the 

 tractus opticus, and winds round to the tubercula quadrigemina. 



The remaining vessels of the brain are derived from the 



Vertebral Artery . 



This artery enters the cranial cavity through the foramen mag- 

 num, and mounts upon the cuneiform process of the occipital bone, 

 where, about opposite to the middle of the medulla oblongata, it 

 unites with its fellow, the two forming a single trunk denominated 

 the basilar artery. The vertebral itself gives off — 1. Posterior 

 arteries to the dura mater. 2. Ramifications to the medulla 

 oblongata. 



The BASILAR artery sends oflT — 



1. The posterior arteries of the cerebellum ; 

 which leave it as it passes under the medulla oblongata, wind up- 

 ward around that body, and cross over to the cerebellum, to the 

 posterior portions of which they are distributed. — The basilar 

 artery then continues its course under the tuber annulare, detach- 

 ing lateral branches as it advances, and from that passes between 

 the crura cerebri, where it bifurcates. Its bifurcations proceed 

 but a short way before each of them subdivide into two vessels : 

 one (2.) runs forward to meet the communicating artery; the 

 other is the 



3. Anterior artery of the cerebellum; which winds 

 outward, around the crura cerebri thence crosses to the cerebellum. 



