30 C. W. M. Poynter 
fig. 10. The arrangement of the branches from the arch is first 
the left common carotid, the right common carotid, the right sub- 
clavian and last the left subclavian artery. In that the left sub- 
clavian is the last branch of the arch and represents in its proxi- 
mal portion the left dorsal aorta, it presents a close analogy to 
the condition of the right subclavian as the last branch, section II, 
ID. it. 
This anomaly is not nearly so frequent as the low right sub- 
clavian, but when we compare it with the total number of right 
arches it is seen to be the usual type of development. It would 
seem that the tendency to develop is stronger in the left dorsal 
aorta than the left fourth arch and that when disturbing factors 
produce this irregularity they more readily affect the arch or 
they act with greater force on the arch, and the persistence of the 
right dorsal aorta may be looked upon as an arrest of the normal 
atrophic process to compensate for the obliterated canal. In the 
case of the low right subclavian, some disturbing factor causes 
an obliteration of the fourth right arch when there is an arrest of 
the normal atrophic process in the right dorsal aorta to com- 
pensate for this obliteration of the canal and insure a circulation 
to the extremity. If it is correct to view the two conditions in 
this light the anomalies are similar in that in each case some fac- 
tor or factors causes the obliteration of an arch which normally 
develops and a compensating development of the right dorsal 
aorta occurs, see figs. 28 and 32. 
The following cases are representative of this type of anomaly: 
Klinkosch (1766), Schleitz (1768), Fiorati (1786), Sandifort (1793), 
Obet (1808), Meckel (1809), Meckel (1816), Otto (1824), Hermann 
(1830) 2 cases, Pommer (1840), Hyrtl (1841), McWhinnie (Quain ’44), 
Quain (1844) 3 cases, Ewen (1845), Tiedemann (1846), Paetruban (1848), 
Greig (1852), Fick (1854), Meyer (1857), Schwegel (1859), Agliette 
(Peacock ’60), Peacock (1860), Tiingel (1862), Turner (1862), Gruber 
(1863) 2 cases, Broader (1866), Bochdalek (1867), Barkow (1869), Cam- 
eron (1871), Watson (1877), Pertik (1880), Brenner (1883) 2 cases, 
Combes-Christopherson (1884), Lockwood (1884), Dittrich (1886), Gott- 
schau (1887), Lane (1887), Lockwood (1800), Herringham (1891), Ab- 
bott (1892), Lunn (1896), Riche (1897), Brachet (1908), Annan (1909), 
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