1905.] 



ARTERIES OF THE BRAIX IX BlUrs. 



115 



text-fig. 20) in which the encephalic arterial system of this bird 

 difters from that of other birds. The anterior spinal is double for 

 a considerable distance behind the origin of the cerebellar arteries ; 

 but I am unable to be precise as to the extent of this double region. 

 The anterior spinal artery is not exactly in the same straight line 

 with the basilar artery, but joins directly the left cerebellar artery. 

 There is thus, as is so often the case, an asymmetry in the cere- 

 bellar arteries ; but the most remarkable peculiarity concerning 

 these arteries is that they rise very near to the circle of Willis, 

 and therefore well in front of the origin of the sixth pair of 

 nerves. 



Text-fig-. 20. 



Brain of Gymnorliina leuconuta (ventral aspect), showing the principal branches 

 of the arterial system. 



Lettering as in text-fig. 15. 



The basilar artery joins the right side of the circle of Willis 

 only. ^ The latter is more elongated in an antero-posterior direction 

 than it is in many birds. 



The posterior cerebral artery among birds usually hides itself 



8* 



