Arterial Anomalies 29 
4. Normal condition of the arches in a case of situs viscerum 
transversus. 
1. I have placed this type first because it would seem to be most 
nearly a simple exchange of the two sides in the normal develop- 
ment, fig. 9. The arch passes over the right bronchus and gives 
off first the innominate, which passes to the left, dividing into 
the left common carotid and the left subclavian, then the right 
common carotid and the right subclavian. It continues down- 
ward as the dorsal or descending aorta and sooner or later as- 
sumes the normal position to the left of the bodies of the ver- 
tebrae. This condition is usual in situs transversus but is occa- 
sionally varied, Hickman (1869). 
I have already shown, section II, A, that it is unusual in cases 
of right arch, or situs transversus, to find the ductus or ligamen- 
tum arteriosum on the right, from which we must conclude that 
the developmental factors for the two arches, aortic and pulmo- 
nary, are quite independent of each other or that the factors de- 
termining the normal type for the pulmonary arch are less easily 
influenced than the other. An examination of the ligamentum 
arteriosum in these cases shows that there are two different dis- 
positions of its distal end. In one type there is a dilation of the 
aorta opposite the third or fourth dorsal vertebra, to which the 
duct or ligament is attached. This dilation represents the vestige 
of the left dorsal aorta, Thomson (1863), Dubrueil (1847), Plate 
II, fig. 1. In the other type the ligament joins the left subclavian 
a short distance from its origin, Bernhard (1818), copied by 
Quain ’44 as Plate VII, fig. 3. In the latter type the proximal 
portion of the subclavian represents the dorsal root of the left 
fourth arch. 
Examples of this class of right aortic arch are not numerous, 
see fig. 29. I have been able to find only the following: 
Cailliot (1807), Bernhard (1818), Breschet (1826), Cruveilhier (1831), 
Quain (1844), Gruber (1846), Drubrueil (1847), Thomson (1863) 2 cases, 
Turner (1883), Vincenzi (1886), Reid (1914). 
2. This condition is found much more frequently than the pre- 
ceding; its development is easily understood by referring to 
257 
