ORIGIN OF THE PULMONARY VESSELS IN THE CHICK. 17 



proliferation for a short distance, forming the pulmonary vein, then breaks up into 

 two vessels which in turn ramify into capillaries that unite with a similar capillary 

 outgrowth formed by the pulmonary arteries. 



Brown (1913), from his observations on embryos of the domestic cat, together 

 with reference to sections of chick embryos, questions the work of Fedorow. He 

 states that the pulmonary system is simply a specially developed part of an indif- 

 ferent plexus originally present in this region, and that the proliferation of endo- 

 thelium described by Fedorow is the left valve of the sinus venosus, which occupies 

 that position. 



In considering these two views it must be remembered that the investigators 

 were using embryos of different forms and that the course of development may 

 vary in these types. My work on the chick can do no more than establish the 

 process as it occurs in that embryo and is designed only for that end. At the same 

 time I feel that this paper tends to show that the views of Brown and Fedorow 

 are mutually exclusive only so far as their interpretations are concerned, 

 not in any actual differences in the mode of development of the pulmonary 

 vein in their respective embryos. That there is a proliferation of endothelium 

 from the dorsal wall of the sinus venosus is apparent. Equally so is the fact that 

 the pulmonary vein is not established at that time. In slightly older stages the 

 pulmonary vein is seen opening into the sinus venosus at that point, and yet in the 

 same section is a mass of endothelium readily recognizable as the left valve of the 

 sinus venosus. Fedorow did not recognize the left valve of the sinus venosus or 

 the dual character of the mass of endothelium giving rise to both the endothelial 

 lip of the left valve and the common pulmonary vein. Brown, from his cat- 

 embryo material, does not exclude the possibility of this origin of the pulmonary 

 vein. He says: 



"It is the purpose of this paper to follow the development of the pulmonary vein 

 of the domestic cat from the early stage in which it empties into the cephalic portion 

 of the sinus venosus in the median line to the stage in which it attains its definitive 

 connections with the left auricle." 



From his work it is clear that in his earliest stage the pulmonary vein is already 

 established and that, instead of offering proof as to the origin of the vein, he is 

 merely describing a stage in its development. Earlier stages might show that in the 

 formation of the pulmonary vein the cat follows the same process as the chick. 

 At least Brown's observations do not exclude such a probability and suggest 

 further work on the cat embryo. 



Brown raised a legitimate objection to Fedorow 's work so far as the left 

 valve of the sinus venosus is concerned, in that the latter observer did not recog- 

 nize the left valve as such nor show its- relation to or origin with the common pul- 

 monary vein. On the other hand, Brown is in error in rejecting Fedorow's work 

 upon the origin of the pulmonary vein, since he based his contention upon findings 

 in a different embryo and at stages that are plainly older than those described by 

 Fedorow. Brown probably saw the endothelial lip of the left valve of the sinus 

 (fig. 5) and the pulmonary vein opening into the sinus and concluded that this 

 was what Fedorow described. 



