XV, 5 
Canizares : Abnormalities of Vertebral Artery 453 
normal, or sixth, cervical transverse foramen, and one where 
the left artery entered the sixth ; the three remaining cases were 
abnormal on both sides. 
On comparing figures it was found that my percentage of 
abnormalities of origin (5 per cent) was slightly higher than 
that of Bean (2.33 per cent). 
Variations in the point of entrance to the transverse foramina 
were relatively much higher. In my collection of cases there 
were fifteen such instances, or 37.5 per cent of the cadavers 
examined. Unilateral variations were almost twice as frequent 
as bilateral ones; namely, 22.5 per cent and 15 per cent, re- 
spectively. 
Table I. — Cases where vertebral arteries had the same point of entrance 
on each side. 
[Six cases, or 15 per cent of those examined.] 
Cervical 
vertebra 
entered. 
Fourth. 
Fifth. 
Seventh. 
Do. 
Do. 
Do. 
Case No. 
14 
22 
1 
4 
7 
8 
Table II . — Cases where vertebral arteries had a different point of entrance 
on each side. 
[Nine cases, or 22.5 per cent of those examined.] 
Case No. 
Cervical vertebra entered. 
Right. 
Left. 
a 36 
Fifth. 
a32 
b39 
Third. 
b38 
Fifth. 
35 
Do. 
37 
Do. 
a 28 
Seventh. 
Fifth. 
31 
34 
Sixth. 
a Vertebral artery enters at higher level on left side. It will be noted that these cases 
constitute one-third of the total number of cases with different points of entrance. 
b Left vertebral arteries arise from the aortic arch. 
DISCUSSION 
The development of the transitory aortic arches of vertebrates 
was first sketched in the chick by Malpighi, as long ago as 1672, 
but the earliest work dealing with their development and trans- 
