Arterial Anomalies 57 
tions, that duct irregularities are independent of arterial varia- 
tions except in so far as developmental disturbances affecting 
the arteries may be so far reaching as also to affect the thoracic 
duct. 
The following is a list of cases illustrating thoracic duct anom- 
alies : 
Duct opening on both sides in cases of low right subclavian: Meckel 
(1772), Cruickshank (1789), Fleischmann (1815), Brown (1882), Hasebe 
(1912). 
Duct opening on right in cases of low right subclavian: Walter (1785), 
Sandifort (1793), Hart (1826), Todd (1839), Stachelroth (1850), Brenner 
(1883) 2 cases, McArdle (1885), Calori (1890), Gladstone & Wakeley 
(1915). 
Right duct persists with or without other anomalies: Hommel (1737), 
Haller (1766), Mascagni (1787), Cruickshank (1789), Fleischmann (1815), 
Meckel (1816), Otto (1824-30), Todd (1839), SOmmering (1841), Teich- 
mann (1861), Thomson (1863), Watson (1872), Combes & Christopher- 
son (1884), Davis (1886), Szalowsky (1888), Reid (1914). 
§X. GENERAL SUMMARY 
From the preceding study certain impressions have been gained, 
which I will present as conclusions; fully appreciating, however, 
that in many cases much needed data was not possible to obtain 
and that the developmental problems are approached from only 
one standpoint. 
There is no satisfactory evidence of a fifth aortic arch in any 
of the anomalies studied. 
Factors disturbing the orderly development of the different 
portions of the vascular system may act independently of and 
without disturbing the normal growth processes. When the gen- 
eral circulatory system is seriously interfered with on account of 
these factors, compensation occurs either through arrest of nor- 
mal atrophic processes or by enlargement of normal channels. 
The factor or factors producing situs viscerum transversus 
seem to be operative on the aortic arch but not on the pulmonic 
arch. 
The study of transposition shows that four separate growth 
285 
