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D. DAVIDSON BLACK 



Blackburn (1) in a few of his cases. The basilar artery is long 

 and gives off numerous irregular branches. Si?^ pairs of these 

 branches arise in the pontine region. The superior and anterior 

 inferior cerebellar arteries arise from a common branch of the 

 basilar. Of the two, the superior cerebellar is much the smaller. 



Fig. 7 Diagram of encephalic arteries pinned out and seen from above. A.b., 

 basilar artery; A.I.C., anterior inferior cerebellar artery; A.s., spinal artery; A.v., 

 vertebral artery; L.P.C., left posterior cerebral artery; M.C.A., median carotid 

 artery; P.C., posterior communicating artery; P.I.C, posterior inferior cere- 

 bellar artery; Sup.C, superior cerebellar artery. X 5. 



Blackburn (q.v.) has noted that when the anterior inferior 

 cerebellar artery is ill developed, the superior cerebellar artery 

 occasionally sends branches to reinforce it. He also noted that 

 when the posterior inferior cerebellar arteries are absent or small, 

 and arising from the basilar, the anterior inferior cerebellar arter- 

 ies send down compensating branches. In this case, both supe- 

 rior and posterior inferior cerebellar arteries are small and the 

 anterior inferior cerebellar arteries are proportionately enlarged 

 and send branches in both directions. 



