Blackburn, Anomalies of Encephalic Arteries. 501 



The Basilar Artery. — This artery, formed originally by coales- 

 cence of the two vertebrals, sometimes contains a septum in its 

 interior, and occasionally shows an incomplete fusion, leaving an 

 opening in the vessel as seen in Case 2009 and in Fig. 2. The 

 vessel is sometimes joined by a large anastomotic branch from the 

 carotid artery. See Case 1926. In my list of cases the basilar 

 showed partial separation into its embryonic components in two 

 cases. It was markedly curved in most cases of enlargement of 

 one of the vertebral arteries, the convexity of the curve being 

 opposite to the enlarged vessel. Nos. 2004, 2063 and 2066. 

 Anomalies of origin of the cerebellar arteries arising from the 

 basilar were common. 



Superior Cerebellar Arteries. — The superior cerebellar arteries 

 were quite constantly represented, sometimes being duplicated. 

 This occurred on the right side four times; on the left twice; and 

 on both sides in two cases. Occasionally this vessel sends branches 

 to reinforce the anterior inferior cerebellar when it is ill devel- 

 oped. 



Anterior Inferior Cerebellar Arteries. — This vessel is quite vari- 

 able in its place of origin from the basilar. The vessel was dupli- 

 cate in eight cases; one or the other was absent in seven; and in 

 live instances it sent large branches to take the place of the pos- 

 terior inferior cerebellar artery when this vessel was small or 

 absent. There seemed to be a constant correlation between the 

 two inferior cerebellar arteries, so that in eighteen cases the two 

 had a common origin in a single trunk arising from the basilar. 



Posterior Inferior Cerebellar Arteries. — This vessel was absent 

 on the right side in ten cases; on the left in six. In these cases the 

 place of the vessel was usually taken by branches from the anterior 

 inferior cerebellar. In a few cases the artery took its origin from 

 the basilar just above the junction of the vertebrals. 



Vertebral Arteries. — One vertebral artery, according to QuAiN, 

 more frequently the left, is sometimes much smaller than the other. 

 The right vertebral was abnormally small in twenty-one cases; the 

 left in twelve cases; both were small in two instances. An unusu- 

 ally large right vertebral with the left about normal in size was noted 

 twice; the two vessels united by a transverse trunk in two cases. 

 The posterior inferior cerebellar artery was large and received prac- 

 tically all of the blood from the cervical portion of the vertebral, 

 in five cases; three times on the right; twice on the left. In these 



