134 



bulletin: museum of compakative zoology. 



Pfl CRD 9. 



digesting fluid, thus leaving the courses of the vessels indicated by the 

 celloidin. From embryos of intermediate size both reconstructions and 

 injections were made, and the results obtained by the two methods 

 compared. 



Observations on Swine. 



In an embryonic pig, whose greatest length as measured in a straight 

 line from the crown of its head to the root of its tail, was between 

 six and seven millimeters, a reconstruction of the primary veins of 



the trunk, when viewed ventrally, ap- 

 peared as in Figure 1. From the ante- 

 rior end of the embryo, two veins, the 

 right and left precardinals (pr'crd. d. 

 and pr'crd. s.), pass posteriorly to the 

 region of the heart, where each is 

 met by a corresponding postcardinal 

 (p'crd. d. and p'crd. s.). The pre- 

 and postcardinals of either side unite 

 to form transverse trunks, the right 

 and left Cuvierian ducts {dt. Cuv. d. 

 and dt. Cuv. s.). The ducts thus formed 

 unite with each other, giving rise to the 

 venous sinus {sn. vn.), through whose 

 posterior wall three large veins enter 

 from the liver, and in whose anterior 

 wall the passage to the heart is seen. 



Of these veins the postcardinals 

 (p'crd. d., and p'crd. s.) claim our 

 special attention. At this stage they are symmetrical. Each begins 

 posteriorly by a union of several small veins at the base of the hind leg 

 of its own side of the body, and in a region dorsal and lateral to the 

 mesonephros (ms'nph.) of the same side. From this region the vein 

 extends anteriorly over the dorsal surface of the mesonephros, penetrating 

 more or less completely the anterior end of that organ, and emerging 

 from it to pass directly, as a well defined blood-vessel, to the Cuvierian 



Figure 1. 



Fig. 1. Reconstruction on a frontal plane of the principal veins and the 

 me^onephroi of an embryonic pig between six and seven millimeters long. Ventral 

 view. X 12. dt. Cuv. d., right Cuvierian duct; dt. Cuv. s., left Cuvierian duct; 

 ,ns'nph., mesonephros; p'crd. d., right postcardinal; p'crd. s., left postcardinal; 

 pr'crd. d., right precardinal; pr'crd. s., left precardinal; sn. vn., venous smus. 



