MEDIAN ANTERIOR CEREBRAL ARTERY 



193 



whole left hemisphere on account of small size and sclerotic obstruc- 

 tion of the anterior communicating artery and the left posterior 

 cerebral artery. 



Fig. 6. Photograph of the base of the brain .showing the origin of a large med- 

 ian anterior cerebral artery. 



The conclusions which I think we may reach with certainty are 

 as follows: 



1. There is a gradual development of the lower mammalian 

 form of azygos anterior cerebral artery into the perfect Circulus 

 Willisii of the human type. 



2. The frequent variations of this system of vessels suggest 

 instability of ontogeny, and of phylogeny. 



3. The anomalies of these arteries together with the presence 



