THE NERVOUS SYSTEM 



1343 



The anterior cerebral artery passes forwards and inwards, and 

 enters the great longitudinal fissure. As it is about to enter that 

 fissure it is connected with its fellow of the opposite side by the 

 anterior communicating artery, which is short, but of fairly large 

 size. Amongst other branches the following are to be noted 

 arising from the anterior cerebral artery : (i) antero-mesial, few and 

 inconstant, and (2) aniero-lateral, both of which pass to the locus 

 perforatus anticus. 



The middle cerebral artery, of large size, sinks into the fissure of 

 Sylvius, which it traverses in an outward direction. Before dis- 

 appearing into the fissure antero-lateral ganglionic branches are to be 



13 15 14- 



Fig. 560. — The Arteries at the Base of the Brain, and the 

 Circle of Willis. 



Internal Carotid 

 Middle Cerebral 

 Anterior Cerebral 

 Anterior Communicating 

 Posterior Communicating 

 Posterior Cerebral 

 Basilar 

 Superior Cerebellar 



9. Transverse Pontine 

 10. Internal Auditory 

 1 [. Anterior Inferior Cerebellar 



12. Posterior Inferior Cerebellar 



13. Vertebral 



14. Anterior Spinal 



15. Posterior Spinal 



16. Anterior Choroid 



17. Posterior Choroid 



18. Central or Ganglionic 



19. Central or Ganglionic 



20. Central or Ganglionic 



(Postero-mesial) 



21. Central or Ganglionic 



(Postero- lateral) 



noted arising from it, which are arranged in two sets, internal striate 

 and external striate, which are destined chiefly for the component 

 parts of the corpus striatum. 



Circle of Willis. — ^This is an important communication between 



the vertebral and internal carotid arterial systems at the base of 



the brain, which is situated around the interpeduncular space. It 



is not actually a circle, though so named, but is a heptagon — that 



I is to say, it has seven angles and seven sides. 



' Commencing at the median line posteriorly, and proceeding 

 forwards on either side to the median line in front, at the great 

 longitudinal fissure, the component arteries of the circle are as 

 ■ follows : (i) the basilar, (2) the posterior cerebral, (3) the posterior 

 I communicating, (4) the internal carotid, (5) the anterior cerebral, 

 \ and (6) the anterior communicating. The connection between the 



