Arterial Anomalies 4I 
identical except for the side affected. In each the common caro- 
tid is absent and the internal and external carotids spring from 
the arch. We may consider that the developmental disturbance 
leading to an atrophy or failure in development of the third arch 
is the primary condition and that the persistence of the dorsal root 
is an attempt at compensation for this anomaly, see fig. 17. 
The following cases are illustrative of the two groups: 
Group II, D, 6. Malacarne (1784) double arch, same condition on each 
arch, Power (Ref. Quain ’44), Kosenski (1867), Macalester (1886), case I. 
Group II, D, 7. Malacarne (1784), double arch; Gottschau (1885) ; 
Macalester (1886), case II; v. Augenmayer (1906), Siegfried (1906). 
8. Obliteration of the third arch and the roots beyond. This 
condition is characterized by the absence of the internal carotid ; 
the condition may occur on either the right or left side and to 
make the classification uniform with the preceding should be di- 
vided into two groups, one for each side. 
Absence of the external carotid is less frequent but does occur, 
Langenbeck (1841). 
All of the following cases are failure of development on the left 
side except that of Todd, which is on the right and Fisher, which 
is on both sides. 
Todd (1787), Koberwein (1810), Quain (1844), Peugnet (1876), Wyeth 
(1878), Flemming (1895), Fisher (1914). 
§ VII 
III. IRREGULARITIES IN DEVELOPMENT OF BRANCHES OF THE AORTA 
This section will include, in addition to the variations in num- 
ber and arrangement of branches springing from the aortic arch, 
anomalous arteries of the ascending aorta. Some of these condi- 
tions are understood embryologically, but many of them are still 
without satisfactory explanation from a developmental stand- 
point; consequently, instead of classifying them from a develop- 
mental standpoint, as has been done in the preceding sections, a 
simple morphological classification will be followed. The ar- 
rangement of branches in many of these groups is similar to type 
forms in other mammalia. It is interesting to note that through 
269 
