321 



Observations on sections. — The sections studied were 

 cut as nearly as possible at right angles to the Aortic arches, since 

 this offered the best opportunity for detecting any branches arising 

 either from the arches, or from the anterior part of the dorsal Aorta. 



The youngest embryos in which was found an arterial circulation 

 to the region of the anterior limb-bud, were those of about seventy- 

 two hours of incubation. In these specimens, the artery supplying 

 the wing-bud appears as a distinct, though irregularly outlined branch 

 from the dorsal Aorta (Figs. 1, 2, 3 scl.a.p). These figures show the 

 connection of the primitive Subclavian with the Aorta in a specimen 

 about eighty hours old. Their relationships may be better understood 

 by a reference to the diagram. Fig. 4, which represents the com- 



d. aoiy 





sei. a. p. 



•w. b. 



"ht. 



Figs. 1, 2, and 3, sections through the -wing region of a chick embryo of eighty 

 hours incubation, showing the primary Subclavian arising from the dorsal Aorta. The 

 sections represent a region öS'/« [J- in thickness (x about 45). Fig. 4, semi-diagramatic 

 drawing of a section through the same region, showing the course of the Subclavian and 

 the independent connection of the Segmental artery with the Aorta. 



d.ao. dorsal Aorta. A«, heart, n. c. neural canal, n. cä. notochord. scL a. ^. primary 

 Subclavian, s.a. Segmental artery, w.b. wing-bud. 



Anat. Anz. XXVI. Aufsätze. 21 



