268 ARTERIES OF THE BRAIN. 



the Circle of Willis.* After sending off these arteries, they 

 continue their lateral direction, and are distributed principally 

 to the posterior parts of the cerebrum. These terminating 

 branches of the Basilar Artery, are called the Posterior Ar- 

 teries of the Cerebrum. 



Arteries of the Brain, which are derived from the Internal 

 Carotid and Vertebral, (see JPlate V. facing page, 268.) 



A. A. The Anterior Lobes of the Cerebrum. 



B. B. The Middle Lobes of the Cerebrum. 



c. c. The Posterior Lobes of the Cerebrum, which rest upon the tentorium. 



D. The Right and Left Lobes of the Cerebellum. 



E. The Medulla OUongata. 



F. The Optic Nerves, cut at their union. 



G. The Corpora Albicantia ; the Infundibulum is seen betwixt these and 



the optic nerves. 

 H. H. The Crura Cerebri. 

 i. The Pons Varolii, or Tuberculum Annulare. 



K. The Eminences of the Medulla Oblongata, called Corpora Pyramidalia. 

 L. The Corpora Olivaria. 



Arteries. 



1. 2. The Right and Left Carotid Arteries, raised with the brain, and cut 

 off as they rise at the point marked in the preceding Plate ; that is, as 

 they rise at the side of the sella turcica. 



3. 4. The Right and Left Vertebral Arteries. 



5. The Union of the Vertebral Arteries to form the Basilar Artery. 



6. The communicating Artery, or Anastomosis betwixt the Basilar Artery 



and Carotid. 



7. The Union of Communication betwixt the carotids of each side by the 



anterior arteries of the cerebrum ; these anastomoses, 6 and 7, form 

 the Circle of Willis. 



Divisions of the Internal Carotid Artery. 



8. The Middle Artery of the Brain passing into the Fissura Sylvii. 



9. The Anterior Artery of the Cerebrum. 



* The arteria communicans is also considered as a branch of the Internal 

 Carotid. The arrangement here alluded to is very remarkable. As the 

 branches which pass off laterally from the single trunk of the Basilar Artery 

 are united to the Internal Carotids, and the Internal Carotids are united to each 

 other, there is an uninterrupted continuation of artery, which encloses a 

 portion of space of a determined form ; but this form resembles an oblong 

 square more than a circle. By this connexion, blood will pass from any one of 

 the four arteries of the brain to all the others. 



