Blackburn, Anomalies of Encephalic Arteries. 503 



Skull thick and dense; symmetrical; sutures and bones normal. Over inner 

 surface of dura of the convexity is a thin neo-membrane of internal pachymenin- 

 gitis. 



Brain. Weight, 1420 grams. Slight general shrinkage over the convexity; 

 veins prominent; arterial branches tortuous. The arteries at the base are sclerotic 

 and present the following anomalies. 



1. Anterior communicating artery double. 



2. At the junction of the upper and middle third of the basilar artery it is joined 

 by a large vessel fully equal to the normal basilar in size, which comes from the 

 left internal carotid just after its emergence from the carotid canal in the temporal 

 bone. This abnormal artery has pierced the dura mater just outside of, and pos- 

 terior to the posterior clinoid process, and dissection shows that it comes from the 

 internal carotid at the junction of the intra-osseous portion with the cavernous por- 

 tion of the vessel. The branch is not at all in the bony canal nor does it pierce the 

 dorsum sellae, though it lies at its origin quite close to the posterior clinoid process. 



The aberrant vessel curves abruptly backward and inward joining the basilar, 

 which is so altered as to appear a part of the anomalous trunk. The large size of 

 the abnormal branch has diverted the basilar from its course and evidently the 

 main blood supply to the posterior cerebral arteries, and the superior cerebellars, 

 came through the anastomatic vessel from the left carotid, the other portions of the 

 basilar and the whole vertebral system being small. The sixth nerve has the nor- 

 mal relation to the carotid artery and the anomalous branch pierces the dura at its 

 anterior and inner side. The other cranial nerves are not in any way interfered 

 with. Complete dissection of the carotid artery outside of the cranium is not per- 

 missible. Two or more minute arteries arise from the anomalous vessel and are 

 distributed to the dura in the vicinity. 



3. The vertebral system presents marked deviation from the normal. The 

 left vertebral is unusually small and the main blood supply from below entered a 

 large trunk which represents both the posterior inferior cerebellar artery and the 

 anterior, no trace of the latter arising at the usual place from the basilar. This 

 common trunk is distributed to the territory of both vessels represented. The right 

 vertebral artery is about the usual size and passes without change of size but with 

 marked curvature into the basilaris. There is no artery on this side corresponding 

 to the posterior inferior cerebellar. 



4. The basilar artery is so changed that the limits of the vessel can only be 

 determined by the junction of the vertebrals and the division into the posterior 

 cerebrals. At about the junction of the middle and lower thirds of the basilar a 

 large trunk is given off which takes the place of the anterior inferior, and posterior 

 inferior cerebellar arteries, the exact reverse of the condition on the left side. The 

 middle portion of the basilaris is small and on the left side gives off the internal 

 auditory artery and some pontine vessels. The upper part of the vessel, scarcely 

 recognizable as such, gives off the superior cerebellar arteries, divides into the poste- 

 rior cerebral arteries, and receives the anomalous carotid branch, as above described. 

 The posterior cerebrals give off the posterior choroid arteries and both are dis- 

 tributed as usual. 



5. The posterior communicating arteries are rather small but their origin and 

 destination are normal. The anterior choroid arteries are normal in origin and 

 distribution and so far as can be determined the other arterial trunks show no 

 anomalies. (Figs. 7, 8 and 9.) 



