ox THE DEVELOPMENT OF THE SUPERFICIAL VEINS 

 OF THE BODY WALL IN THE PIG. 



HELEN WILLLSTON SMITH. 

 From the Anatoiiiivul Lahoratonj of the Johns Hopkins University. 



With 11 Figures. 



Satisfactory studies of the vascular system of young embryos 

 have been impossible until quite recently, for the embryologist has 

 been unable to see much more than mere fragments of the growing 

 ends of this system in embryos treated by the usual methods of prep- 

 aration. During the past few years the method of injection of the 

 vascular system of young embryos has been perfected more and 

 more in this laboratory, so that now we are able to procure complete 

 injections in the very youngest stages. In order to make proper 

 headway in the study of the morphology of the vascular system it 

 is necessary to study the development of the primitive vessels in the 

 embryos. For instance, more fundamental conditions can be ob- 

 tained for the study of development in the umbilical vein, than 

 in the vessels of an organ ; in the former case there is but one vessel 

 to be followed, while in the latter there are millions, and it is 

 practically impossible to find the same terminal twig from stage to 

 stage. 



The key to the situation is obtained when the main trunks and 

 all their branches are brought out sharply by means of injection 

 in their very earliest and in subsequent stages. This has now 

 been accomplished by a number of investigators in this laboratory, 

 most successfully, probably, by Dr. Evans, who injected many of 

 the embryos I have studied. 



In order to obtain perfect injections it is necessary to inject live 

 embryos, and, in addition to tadpoles and chicks, an abundance of 

 The American Jouknal op Anatomy. — Vol. IX, No. 3. 



