62 



In yet another work (24) upon which our figure two is based 

 De Vriese says that in the course of embryonic or postembryonic 

 development, the internal carotid, no longer sufficing for the vascular 

 supply of the brain, has been reinforced by an artery anastomosing 

 with it — the a. basilaris — which has resulted from the union of 

 the vertebrals; and which secondarily undertakes the supply of the 

 brain posterior to the internal carotid, with a consecutive atrophy of 

 the proximal portion of the a. cerebri posterior intermediate between 

 its origin from the a. carotis interna and its point of union with the 

 a. basilaris, the part which in human anatomy is called the a. com- 

 municans posterior. (See Fig. 2.) 



The above extracts from the work of two such competent observers 

 as Beddard and De Vriese have been somewhat long, but they are 

 of vital importance, as from them we are enabled to make the follow- 

 ing instructive deduction. 



The arterial supply to the brain is primitively derived from the 

 internal carotids. As the brain evolved and became larger, particularly 

 in its occipital region, this supply has no longer sufficed, and there 

 has been added an additional supply from the subclavians by way of 

 the vertebrals. Batujeff's variation, as well as our own case, are 

 variations in this more recently superadded portion of the brain's 

 arterial supply. They are therefore, in all probability, not to be 

 regarded as cases of atavism, nor of progression, but of instability of 

 the more recently superadded blood supply. 



We turn next to an examination of the rarity of this variation. 

 Many observers have examined the circulus arteriosus (Willisi) and 

 as it is perfectly safe to assume that had they noticed a case of 

 nonunion of the aa. vertebrales they would have mentioned the fact, 

 we may state that in a recorded examination of 1619 cases there have 

 only occurred two examples of nonunion of the aa. vertebrales in the 

 a. basilaris, namely, Batujeff's example already quoted and this present 

 instance of our own. Our figures are derived from the following 

 sources : 



Blackburn (15) 



Cavatorti (13) 



Fawcett and Blatchaord (25) 



Longo (26) 



Barbieri, quoted by Longo 



LoMBROSo, quoted by Longo 



Frigerio, quoted by Longo 



Mori, quoted by Longo, and (30) 



