324 



between the base of the wing and the lung, it forms a juncture with 

 the primary Subclavian, the latter coming from the dorsal Aorta. The 

 fore-limb at this time occupies a position posterior to the heart, which 

 necessitates a comparatively long course for the secondary artery to 



iv. b. '■-<■'' ,.'=w. r. ^'^ ~~ ""'" ^,-scL a. p. 



d. ,10. ,-. "-"' '^- bt ' '•'^ _^-''w. r, 



d. aa "'r-"-''' 



^0- 11 



_,.--, set. a. p. -'■" ,--scl. a. p. 



til. b. vC ,-'-w. r. IV. b. --' — '" / _,,-'«'. r. 



' '^•^o . ,---'' \ d. ao - ,--'''' 



\Z. 15. 



<W. b. ', y ■ 'O). b. 



14. 



Figs. 10, 11, 12, and 13, sections through the wing region of a chick embryo of 

 five days of incubation, showing the condition of the primary wing artery at this age. 

 The Segmental artery now arises on the same stem as the Subclavian, and the roots 

 of the latter have a more dorsal position on the walls of the Aorta than in the earlier 

 specimens. The sections, Nos. 1, 2, 4, and 8 on the slide, rejjresent a thickness of 

 106 Vg Ml (x about 25). 



Fig. 14, semi-diagramatic representation of the above conditions. Reference letters 

 as in preceeding figures. 



