Arterial Anomalies 55 
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SIX 
IV. THE VARIATIONS IN THE DEVELOPMENT OF THE THORACIC DUCT 
Anomalies of the thoracic duct are considered in this paper 
because they frequently appear in conjunction with the cases of 
low origin of the right subclavian artery. Calori (1890) has 
studied this condition and concludes that there is no relation be- 
tween the two anomalies; with this conclusion I am agreed be- 
cause an analysis of the cases of low subclavian shows that only 
a part of them also have an anomalous thoracic duct and that 
the type of irregularity is not constant and may be found in cases 
with no other developmental defect. 
The irregularities in the position and number of connections of 
the left duct with the venous system are matters of common 
knowledge and need not be reviewed; we will confine this review 
to the cases in which all or a part of the system opens into the 
veins on the right side. 
. We are quite sure that the thoracic duct begins as a paired 
structure in relation to the two dorsal aortae and that the single 
duct is the result of a fusion of the two ducts in somewhat the 
same manner as the single dorsal aorta is formed. More obser- 
vations are needed at the cephalic end to determine whether the 
right duct normally develops as the right aorta does and disap- 
pears by a similar atrophy. The embryonal history may be il- 
lustrated if we may consider these cases of arrested development, 
or rather development in the type of embryonal stages. Som- 
mering (1841) saw a case in which two ducts ran from the re- 
ceptaculum chili to the venous angles in the neck, one duct open- 
ing on the right and one on the left. In Duval’s (ref. Todd ’39) 
case the duct was double in the abdomen. Butler (1903) saw a 
case in which the duct was double in the thorax, then single for 
about an inch opposite the third thoracic vertebra, then continued 
as two separate ducts, one opening on the left and the other on 
the right. Numerous examples have been reported in which both 
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