366 C. V. MORRILL 



embryo of 7,8 mm. Lewis ('03) mentions a splitting of the 

 anterior cardinal vein near its entrance into the duct of Cuvier, 

 the subclavian vein arising from its outer part. A comparison 

 of his Plate IV and Thyng's ('11) figure 2, with figures 5 and 6 

 of the present paper seems to indicate that this process is normal 

 for the pig embryo. 



In conclusion I wish to express my thanks to Prof. H. D. 

 Senior who kindly suggested a re-investigation of the atrial 

 septum and to Prof. F. W. Thyng for advice and criticism. 



