Blackburn, Anomalies of Encephalic Arteries. 495 



number of diagrams of associated anomalous conditions which are 

 for the most part self-explanatory. I would, however , call attention 

 to the number of these in which surgical ligation of the internal 

 carotid, or obstruction of the vessel by thrombosis would endanger 

 the whole hemisphere. 



It will be noted in these diagrams, and in a number of the cases 

 in the list, that anomalous conditions are frequently associated. 

 In the sixteen cases diagramed this was strikingly manifested, and 

 at the same time there is a certain correlation between some of the 

 anomalies, notably in enlargement of the anterior cerebral of one 

 side and small size of the opposite vessel; enlargement of a pos- 

 terior communicating artery with underdevelopment of the corre- 

 sponding posterior cerebral; and in increased size of the opposite 

 vertebral when one of these is undeveloped. 



In the list of cases, 227 were included — Nos. 1968-2194 — but in 

 some of these the brain was not examined, leaving 220 consecutive 

 cases in which the vessels were studied. This number and order 

 of cases I think may be taken as fairly representative of the rela- 

 tive frequency of arterial anomalies among the insane, and, though 

 the number is too small for valuable statistics on this question, it 

 may be taken as showing the frequency in the several forms of 

 mental disease. 



In the 220 cases studied, 65 showed no anomalies, slight dispar- 

 ity in size of the paired vessels being disregarded, and no anomalous 

 conditions being noted unless presenting a deviation beyond the 

 normal variation. 



Professor Windle, who studied the vessels in 200 cases among 

 those presumably sane, found 76 cases normal, and disregarding 

 slight difference in the size of the paired vessels he found 119 cases 

 normal in number and arrangement. As I have included the 

 cerebellar arteries in my list, while Windle studied only those of 

 the circle of Willis, this must be taken into consideration in com- 

 paring the two final results. 



As I shall have to make frequent reference to the statistics of 

 Windle, for comparison with my own, I would here acknowledge 

 my indebtedness. 



SUMMARY. 



Internal Carotid Artery. — The internal carotid artery has been 

 quite constant in size and development in my cases. It is all the 



