210 



HITCHCOCK'S ANATOMY 



passing through a foramen or opening in the transverse process 

 of each of these vertebrae, at last reaches the posterior portion 

 of the brain. This artery in the brain meets with the termi- 

 nal branches of the internal carotid, so that the blood can 

 easily reach the brain from either direction. By this ar- 

 rangement, if, from pressure or accident, the flow of blood 

 to the brain in either of these channels should be obstructed, 

 the other would supply it ; for sensation and consciousness 



Fig. 213. 



Circle of Willis. 1, Vertebral Arteries. 2, 3, Anterior and Posterior Spinal Arteries. 

 4, Posterior Meningeal Artery. 5, Inferior Cerebellar. 6, Basilar. 7, Superior Cerebel- 

 lar. 8, Posterior Cerebral. 9, Branch of Carotid. 10, Internal Carotid. 11, Ophthalmia 

 Artery. 12, 13, Cerebral Arteries. 14, Anterior Communicating Artery. 



entirely cease if the brain be deprived of its arterial blood. 

 This arrangement is called the " Circle of Willis" from its 

 discoverer. 



What arteries does the Vertebral communicate with in the brain ? What is the ser- 

 vice of this arrangement? 



