VEINS AND LYMPHATICS IN TRAGULUS 199 



involved in the formation of the hepatic sinusoids, it is still possi- 

 ble to recognize two well defined venous channels passing through 

 the liver, parallel with the body axis and situated in the angle 

 formed by the junction "of the dorsal and mesial hepatic surfaces. 

 The anterior walls of these channels are subject to great irregu- 

 larities occasioned by their relations to the hepatic sinusoids; 

 their dorsal and mesial walls are well defined. Each channel 

 is situated opposite the coelomic angle, dorso-lateral to the gut 

 tube, directly ventral to the sub-cardinal vein and ventro-mesial 

 to the post-cardinal vein. The two intra-hepatic vitelline vessels 

 not only drain the sinusoids of their respective sides but commu- 

 municate with each other by several transverse anastomoses which 

 follow a semi-circular course in front of the gut tube. The most 

 cephalic of these anastomotic channels is the largest and lies at 

 a level a little below the vitelline entrance into the sinus venosus. 

 As it approaches this sinus, each vitelline vein undergoes a change 

 in course, curving outward and forward, then upward and in- 

 ward to a point slightly mesial to the entrance of the umbilical 

 vein. The intra-hepatic vitelline channels may be traced cau- 

 dad to a large sinus-like blood space situated immediately below 

 the liver. This large sinus has been greatly augmented by the 

 confluence of the two umbilical veins and the omphalic portions 

 of the vitellines. From its position it may be conveniently 

 referred to as the sub-hepatic sinus (fig. 6, 11), which, in this 

 embryo, receives blood from the large umbilical veins and a 

 single omphalic vessel of medium size. It delivers blood to 

 the hepatic sinusoids, and the two intra-hepatic vitelline chan- 

 nels, having a more ample communication with the channel of 

 the right side. Two veins of small size appear in the gut wall 

 in regions below the liver; their relations identify them as the 

 mesenteric veins. The left mesenteric vein is the larger of the 

 two; it establishes connection with the left intra-hepatic vitel- 

 line channel at a distance of 100/* cephalad of that vessel's de- 

 parture from the sub-hepatic sinus. The right and smaller 

 mesenteric vein joins the left vein by a semicircular anastomosis 

 behind the gut at a point 300/x below the entrance of the latter 

 vein into the left intra-hepatic vitelline channel. The follow- 



