158 A MANUAL OF ANATOMY. 



eluded from the central cavities of the brain, as will appear 

 later. 



The Blood Supply of the Brain. Figs. 10 and 21. 



The brain receives its supply of blood through the inter- 

 nal carotids and vertebral arteries. 



After entering the skull through the foramen lacerum 

 medium the internal carotid artery passes forward through 

 the cavernous sinus as given on page 43. At the anterior 

 part of the sinus the artery turns upward through the dura, 

 behind and internal to the anterior clinoidal process, and 

 reaches the base of the brain at the beginning of the fissure 

 of Sylvius, where it divides into the anterior and middle 

 cerebral vessels. 



The vertebrals, after entering the skull through the 

 foramen magnum, are found at the side of the medulla. 

 They converge as they pass forward and unite in the middle 

 line at the junction of the pons and medulla to form the 

 basilar artery. 



The basilar artery runs forward in a median depression in 

 the pons to its anterior margin, where it divides into the two 

 posterior cerebral vessels. 



The Circle of Willis. Figs. 21 and 22. 



The anterior cerebral arteries pass forward and inward 

 to the beginning of the great longitudinal fissure, which 

 they enter. They continue upward and backward over the 

 corpus callosum, distributing branches to the inner surface 

 of the hemisphere as far as the parieto-occipital fissure 

 (where the terminal branches anastomose with similar 

 branches from the posterior cerebral arteries). 



At the beginning of the great longitudinal fissure the 

 anterior cerebral vessels are united by a very short artery 



