The Arteries Forming the Circle of Willis.

So far as I &m awaie, no attempt has been hitherto made to clasify the abnormalities and variations of the larger cerebral arteries, as the result of observations made on anything like an extensive scale. Quain, in his otherwise exhaustive work, devotes but a very short space to these vessels, and other authors have followed his example. I have been for some time collecting statistics on this subject, and published a few years ago a preliminary note, in which the conditions met with in sixty-five cases were described. The number of those of which I have information now amounts to 200, and the results obtained seem now to be worthy of record. I have examined the majority of these myself; for those which I have not seen I have to rely chiefly upon the careful notes made for me by friends who have occupied the position of pathologist to the General Hospital in this town, to whom, as to my friend and assistant Dr Hogben, who has also favoured me with information, I have to express my obligations. In seventy-six of the cases, the condition which obtained was strictly that which is described in the text-books as the normal arrangement. In forty-three, however, of those reckoned as abnormal, the only deviation was a more or less well-marked disproportion between the posterior communicating arteries of the two sides. If we disregard this condition, we may say that in 119 cases out of 200, the normal number and arrangement of the arteries was present. I shall describe the variations under the head of each of the arteries forming the circle seriatim; in so doing it will be impossible to avoid a certain amount of repetition. Anterior Communicating Artery.-In 159 cases this vessel