xv. 5 Canizares: Abnormalities of Vertebral Arte))/ 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 13 per cent of those examined.] 



Case No. 

 14 



22 



1 

 4 



7 

 8 



Cervical 

 vertebra 

 entered. 



Fourth. 



Fifth. 



Seventh. 



Do. 



Do. 



Do. 



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.] 



i 



Case No. 



Cervical vertebra entered. 



Right. 



Left. 



»36 -. - 



Fourth 



do 



Fifth. 

 Seventh. 

 Third. 

 Fifth. 



Do. 



Do- 

 Seventh. 

 Fifth. 

 Sixth. 



*32 - 



b39 



Sixth 



b38 



..do 



35 



..do 



37 





=>28 



do 



31 



Seventh 



do 



[ 34 







11 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- 



