58 GC: WME Pownier 
centers, viz., truncus arteriosus, bulbis cordis, ventricular limb 
and arterial limb, must be considered and that any one or more 
may show irregular development while the remainder develop 
normally. 
It would seem that the tendency to develop is stronger in the 
left dorsal aorta than in the left fourth arch if we may judge 
from the more frequent type of right aortic arch. 
Factors disturbing vascular development apparently act at a 
very early stage and on a very restricted area. In interpreting 
anomalies we should attempt to fix the time and position of dis- 
turbance if we are to throw light on the factors themselves. 
There is insufficient embryological data to explain many of the 
anomalous arrangements of the branches from the aortic arch and 
it would seem that these problems might be solved by a study of 
the lower mammals, in which these anomalies are type forms. 
There is no way of determining accurately the percentage fre- 
quency of the various anomalies in relation to the normal; the list 
below shows the percentage in relation to the total number of ab- 
normalities noted. In securing these figures I have divided the 
irregularities into two groups one, sections I and II, relating more 
Group I 
Percent. 
Irregular development of the aortico-pulmonary septum..... VES 
Atresiavoni the pulmonanyaarteiyareue sciences eee 6.8 
Transposition of aorta and pulmonary artery .............. GG 
Patent tductuspartentosusinsracer ccm crc eee 20 
Doublesaorticanchee sys ss sie cee yrs ee Stes a ee 2.2 
Right: aortiovar clin ese eis snes cate ce acl le Ree ERG he meen 9 
Lowrsonginvor rightusubclayianeantenyacs een eerie 31 
Absence.ot thesthind arch hance) aaa eee nee 2 
Group 2 
Onetbranchiitromvcaonticiarchwaareee ere eet ee 3 
Bizinnominate: ntrunks were seen i ee ee eee ee EIne 3 
Bi-carotid strum ys Sore celia a ete ORGN Ee pg run tee ah wri aa aa 25 
Metticarotidsiromythe innominates ieee ce eee 20 
No innominate stem. (Low origin of subclavian notincluded) 8 
ettivertebralutnomeaortic anche er eer tee 30 
Rightivertebralerrompaonticeanch mms iia. ween 4.7 
Unusualibranchesstromuthelaontic anche eee 2.5 
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