A CASE OF CYCLOPIA 203 



Anteriorly the basilar artery becomes continuous with a large 

 left posterior cerebral vessel. No right posterior cerebral artery 

 is present. A small median branch passes forward at the point of 

 origin of the left posterior cerebral artery. This vessel is to be 

 considered as a single posterior communicating artery. It is 

 represented in figure 50 as being much larger than is actually 

 the case. 



From the median carotid trunk the cerebral vessels radiate 

 out in such a manner that they become distributed to the right 

 side and anterior portion of the left side of the cerebral vesicle. 

 The posterior portion of the cerebral vesicle on the left side is 

 supplied wholly by the posterior cerebral branch of the basilar 

 artery. 



From the vertebral arteries posteriorly to the point of origin 

 of the common trunk of the superior and anterior inferior cere- 

 bellar arteries, the encephalic vessels have shown but little vari- 

 ation from the normal condition and may be identified with a 

 reasonable degree of certainty. 



Beyond this point there has been a very marked disturbance 

 in the origin and relations of the various vessels supplying the 

 cerebral vesicle. 



Mall (14) has shown that under normal circumstances the 

 arrangement of the encephalic vessels arising as branches from 

 the future circle of Willis varies remarkably at different stages 

 in the growth of the embryo. 



Anomalies of the encephalic vessels are very commonly met 

 with among the insane (1), more so than among normal individ- 

 uals. The above fact implies that the growth and arrangement 

 of these vessels is influenced in no small degree by the growth of 

 the cerebral tissue. Very slight anatomical variations in the latter 

 increase the tendency toward vascular anomalies. 



When, as in the case in point, there has been a profound dis- 

 turbance in the development of the primary forebrain vesicle a 

 correspondingly wide deviation from the normal arterial arrange- 

 ment may be looked for. The anomalies will be partly due to 

 the mechanical difficulties encountered in growth, but mostly to 

 the absence of certain parts of the cerebral tissue itself. 



