464 



Mabel Bishop 



trunk to the other is probably a portion of the fifth arch that lias per- 

 sisted, for its origin from component A is above the semi-lunar valve 

 and its insertion into component B is below the normal aortic arch. 

 It has no connection with the pulmonary S5-stem, and therefore cannot be 

 a portion of the sixth arch. The dorsal origin of the right subclavian 

 is an anomaly of common occurrence (Quain), but the present case differs 

 from the nsual condition under such circumstances in that the dorsal 

 portion utilized in forming the subclavian also gives rise to the right 



Text Fig. 2. Diagram showing 

 arterial ai'ches in Teras XII. 



the transformations in the primitive 



vertebral, whereas usually, under a like condition, the anterior portion 

 of the right fourth arch becomes the vertebral. The first, second and 

 third arches are obviously normal, but in duplicate. Such an embryonal 

 vascular condition, although suppositional, would fix the future develop- 

 ment of the organism of which it is a part, and, it seems to me, would 

 terminate in such an adult condition as exists permanently in Teras XV. 

 The next and final cosmobion in the series that I have to present will 

 demonstrate the hypothesis that as the doubling extends farther and 

 farther posteriorly, the heart becomes more and more involved. This 



