Blackburn, Anomalies of Encephalic Arteries. 497 



In a few instances the two arteries have fused anterior to the 

 anterior communicating artery leaving a triangular opening be- 

 tween the vessels. Nos. 2073, 2077, 2139 and 2141 show this type 

 of anomalous development. 



Other anomalies of these arteries are occasionally met with. 

 The vessels may both arise from one carotid as distinct trunks, 

 one of which may be joined by an undeveloped vessel represent- 

 ing the opposite artery, or this vessel may be completely absent. 

 Sometimes both vessels arise from one carotid by a single trunk 

 which may or may not be joined by an abortive branch represent- 

 ing the opposite vessel. This condition must, however, be care- 

 fully analyzed as it is not essentially different from the conditions 

 represented by Nos. 2004 and 2066; especially if the vessels divide 

 at the situation of the anterior communicating artery. 



The important surgical complications which would arise in 

 these anomalous developments of the anterior cerebral arteries 

 will be readily comprehended by reference to the accompanying 

 diagrams of combined anomalies. 



In my 220 cases the anterior cerebrals were fused into a common 

 trunk in seven cases; see examples Nos. 2073, 2139 and 2141. 

 This condition seemed at first sight to be more frequent as one of 

 the vessels was not infrequently quite small and sometimes prac- 

 tically impervious, so that the vessels appeared as one trunk arising 

 from the carotid. Nos. 2004, 2057, 2063, 2066, 2073, 2099 and 

 2137 show this type of anomaly. 



In the list ten cases showed the right artery small and the blood 

 supply coming from the opposite carotid; in six, the left was the 

 defective vessel. In one case the right artery was unusually large 

 while the left was normal; and in five instances a large recurrent 

 branch originating commonly from the anterior cerebral at its 

 junction with the anterior communicating turned backward and 

 supplied the third frontal gyrus and the insula. 



WiNDLE found eight cases of fusion of the anterior cerebral 

 arteries; and two instances of absence of one vessel, the place of 

 the missing trunk being taken by a small branch from the opposite 

 carotid. I have not regarded these cases as absence of the vessel 

 in question, but as instances of underdevelopment with compen- 

 satory enlargement of the opposite trunk and the anterior com- 

 municating artery. See Nos. 2066, 2077, 2099. 



Anterior Communicating Artery. — The anterior communicating 



