Lilian V. Sampson 491 



teriorly, bathe the head-kidneys and empty into the Cuverian veins (Pig. 

 H8-1, pcv, cv). The posterior cardinals are remarkably conspicuous 

 from stages VI to IX, and- persist to stage XII, when only vestiges of 

 them can be found posterior to the degenerated head-kidneys. 



The anterior cardinals (Fig. L, acv) also empty into the Cuverian 

 veins. After the degeneration of the posterior cardinals, the Cuverian 

 veins and anterior cardinals persist as the anterior venje cavse. After 

 stage VII, the inferior jugular veins from the ventral region of the 

 neck enter the Cuverian veins with the cutaneous, and persist after the 

 cutaneous veins have been reduced. In stage XV, they are present as 

 branches of the anterior venae cav£e. 



Fig. O. Sag-ittal section of stage XII (drawn to same scale as Fig. Bl). ao, aorta ; au, au- 

 ricle; b, bladder; bd, bile duct; da, dorsal aorta; g, gut; k, kidney; 1, liver; lu, lung;'ma, 

 mesenterial arterjs oe, oesophagus; p, pancreas; pvc, posterior vena cava; sv, sinus 

 venosus ; ta, truncus arteriosus ; v, ventricle ; vv, vitelline vein. 



The posterior vena cava appears at about stage VI, as a median vein, 

 which passes along the dorsal wall of the liver, receives the vitelline vein, 

 and empties into the sinus venosus (cf. Pig. II7-2). As the vitelline 

 vein becomes less prominent the vena cava increases in importance, and 

 takes its place as the posterior end of the sinus venosus. In later stages, 

 as the heart becomes separated from the liver, the posterior vena cava 

 is also separated from the liver (Pig. 0) and receives definite efferent 

 vessels from it. The posterior vena cava joins the right posterior cardinal 

 (Pig. He, 7, pvc, pcv) at a little distance anterior to the union of the 

 two cardinals; and after the posterior cardinals disappear, continues to 



