Blackburn, Anomalies of Encephalic Arteries. 505 



It would seem probable that in this case we had both the formation of the aneu- 

 rism and the hemorrhage in part dependent upon arterial overstrain consequent to 

 the lack of anastomoses between the right side and the left. The enlargement of 

 the right posterior communicating artery seems to be a direct compensation for 

 the small size of the posterior cerebral, but the small size of the right anterior cere- 

 bral and the current in the anterior communicating artery would effectually pre- 

 vent relief to overstrain in this direction. Certainly the left carotid had a much 

 freer outlet for its contents than the right, but at the same time owing to the com- 

 pensation present the two hemispheres probably received a normal supply of blood 

 until the complications due to arterio-sclerosis supervened. (Fig. 11.) 



CONDITION OF THE ENCEPHALIC ARTERIES IN FORTY OF THE TWO 

 HUNDRED AND TWENTY CASES. 



Case 1973. R. M.; colored; male; aged 6i; paresis. Arterio-sclerosis. Right anterior cerebral 

 artery small, and the larger portion of the blood came from the left side. From the anterior communi- 

 cating artery onward, the left anterior cerebral artery forms a large trunk which afterwards divides 

 opposite the genu callosi into two callosal arteries. Left posterior inferior cerebellar artery absent; 

 right small. 



Case 1974. E. N.; white; male; aged 76; chronic dementia. Arterio-sclerosis. Right posterior 

 communicating artery very large; the corresponding posterior cerebral small; post choroid artery arises 

 from the right posterior communicating artery. Left posterior communicating artery rather large; 

 posterior cerebral of this side small. Anterior communicating artery small and practically impervious. 

 Right vertebral artery very small and separates into two branches, one of which forms the posterior 

 inferior cerebellar artery; one of which joins the basilar. 



Case 1980. L. F.; colored; female; aged 40; manic-depressive insanity. The right posterior 

 communicating artery large and furnishes the main blood supply to the posterior cerebral region, this 

 artery being quite small. The left anterior cerebral artery is larger than normal and sends its blood 

 supply to the opposite artery through an enlarged anterior communicating artery. The right anterior 

 inferior cerebellar is double; the opposite artery comes off the basilar by a common trunk with the 

 posterior inferior cerebellar, and supplies its region, the proper artery being very small. 



Case 1985. W. E.; white; male; aged 65; senile dementia. Arterio-sclerosis. Left posterior 

 communicating artery very large and is distributed to the inferior temporal regions. The posterior 

 cerebral artery of this side does not join the former, but is distributed to the parts around the crus 

 and the choroid plexuses. The left anterior cerebral artery rather small, the main blood supply com- 

 ing from the opposite artery. 



Case 1986. D. L.; colored; male; aged 95; senile dementia. Arterio-sclerosis. Both posterior 

 communicating arteries very large; post cerebral arteries extend forward and join them at an acute 

 angle. Anterior communicating artery absent. Right superior cerebellar artery double. 



Case 2000. L. T.; colored; male; aged 82; senile dementia. Arterio-sclerosis. The right anterior 

 cerebral artery extremely small both anterior cerebral arteries being supplied from the left side. Anterior 

 communicating artery double. Right posterior communicating artery very large and the posterior 

 cerebral joins it about its middle as a small vessel. (Fig. 3.) 



Case 2004 W. L.; colored; male; aged 50; chronic dementia. Arterio-sclerosis. Right anterior 

 cerebral very small at its origin, both anterior cerebral arteries appear to come from the left side. No 

 true anterior communicating artery exists. After turning around the genu callosi the anterior cerebral 

 arteries are distributed as usual. Right posterior communicating artery small; left larger than normal. 

 Right vertebral artery very small; posterior inferior cerebellar artery of this side represented by a small 

 thread and an impervious branch from the common trunk with the anterior inferior cerebellar artery. 

 On the left side a double anterior inferior cerebellar artery is present, and a double superior cerebellar. 

 (Fig. 3-) 



Case 2009. S. W.; white; male; aged 66; chronic epileptic dementia. Senile arterio-sclerosis. 

 Both vertebral arteries, about equal in size, join at the upper end of the medulla, and again separate, 

 making a fenestra in the basilar about one-half an inch in length. The right posterior inferior cerebellar 

 artery is normal in position, the left arises at the first point of junction of the vertebrals. The two 

 anterior inferior cerebellar arteries arise from the right and left division of the basilar respectively. 



