496 Journal of Comparative Neurology arid Psychology. 



more remarkable that in several reported cases, a large anomalous 

 branch has been found arising from the cavernous portion of the 

 vessel and turning abruptly backward, joining the basilar. A 

 case of this interesting anomaly is given somewhat in detail in Case 

 No. 1926, Figs. 7 to 9. A case of direct union of the carotids with- 

 out the intervention of an anterior communicating artery is given 

 by Mitchell and Dercum; this I have not met with, though 

 direct fusion of the anterior cerebrals, a closely allied condition, has 

 been seen a number of times. Occasionally some disparity in 

 size of the two vessels is seen, but it was deemed noteworthy in 

 only one case. 



Middle Cerebral Arteries. — The middle cerebral artery does not 

 enter into the circle of Willis, though the circulation in it is 

 markedly influenced by anomalies of its component vessels. A 

 few abnormal branches were noted, and in one case the inferior 

 external frontal branch was absent and its place was taken by a 

 recurrent vessel from the anterior cerebral. As a result of this a 

 large thrombotic softening of the Sylvian region did not affect the 

 third frontal convolution and speech was preserved. Cases have 

 been recorded of abnormal origin of the vessel itself, and of origin 

 of the post communicating artery and the anterior choroid from 

 this artery, but I have found no case which could not be otherwise 

 explained. 



Anterior Cerebral Arteries. — The most common anomaly of the 

 anterior cerebral arteries is the enlargement of one artery and a 

 corresponding small size of the opposite artery. As the result of 

 this the main blood supply comes through the enlarged vessel, the 

 anterior communicating artery is enlarged, and both anterior 

 cerebrals appear to arise from one carotid. Sometimes the ante- 

 rior communicating artery remains distinct, but it may be com- 

 pletely merged into the anterior cerebrals and the remnant of 

 the small undeveloped anterior cerebral join it at an acute angle. 

 Nos. 2057, 2063, 2066, 2099 and 2137 represent this type of 

 anomaly. Another modification of these arteries is their fusion 

 into a common trunk from the site of the anterior communicating 

 artery onward to the vicinity of the genu callosi, where they 

 commonly again form the two anterior cerebral trunks with 

 a normal distribution. In this condition there is no proper 

 anterior communicating artery. Sometimes the anterior cerebral 

 of one side is very small, in some the vessels are about equal in size. 



