318 



showing the arterial transformations in birds, to the year 1890, no 

 satisfactory account of the origin of this artery was given; notwith- 

 standing Mackat's large paper, which was especially concerned with 

 the origin of the Subclavians and Carotids of birds. Several attempts 

 have been made, by Sabatier and others, to reconcile the position of 

 the Subclavian in its development with the adult anatomical relation- 

 ships; but the schemes do not agree with one another, or with the 

 facts as now known, 



HocHSTETTER ('90) greatly cleared the question by pointing out 

 that, while the definitive Subclavians arise from the ventral ends of 

 the third Aortic arches, as maintened by Mackay, there are also 

 primary arteries to the wing-bud which have their source directly from 

 the dorsal Aorta. This earlier formed vessel, present only in the 

 early embryonic stages, completely disappears, and it is regarded by 

 HocHSTETTER as the homologue of the Subclavians in mammals. 



Hochstetter's paper, though clear in its main points, is illustra- 

 ted only l)y a few diagrams. It is, therefore, desirable that the question 

 should receive further attention, and that figures showing the actual 

 condition should be published. 



Review of literature. — Preliminary to an account of the 

 present observations on the Subclavian of the chick, a brief review of 

 the literature of the subject will be given. 



Karl Ernst v. Baer ('28) was the first to present a scheme 

 for the development of the Aortic arches in the birds, in which the 

 Subclavian is shown as arising from the dorsal end of the third arch. 

 Sabatier returned to this conception in making his diagrams in 1874. 



The scheme ofRATHKE('57) for the development and transformation 

 of the Aortic arches in the birds afforded the first generally accepted 

 explanation of the origin of the Subclavian in that class of verte- 

 brates. In this diagram, the Subclavian is represented as arising from 

 the dorsal end of the fourth Aortic arch ; whence he supposed that it 

 gained its adult position through a shortening of the fourth arch, and 

 a coalescence of the Subclavian root with the common Carotid. The 

 latter he derived from the ventral connection between the third and 

 fourth arch. This scheme of development has proved inadequate to 

 reconcile the fact that the Subclavian in birds is not, as in mammals, 

 dorsal to the Vagus nerve and the superior Vena cava, but ventral 

 to those structures. 



Sabatier ('74) in his modification of Rathke's scheme of the 

 development of the Subclavian artery in birds, also disregarding the 

 adult relationships of the Vagus nerve and the superior Vena cava to 



