220 HISTOLOGY. 



blood vessels. Surrounding the entire liver close to the hepatic trabeculae, 

 the septum transversum produces the dense fibrous capsule [capsule of 

 Glisson]. The fibrous capsule is covered by the tunica serosa everywhere 

 except at the mesenteric or ligamentous attachments. Thus the trans- 

 verse septum produces the diaphragm, the falciform and triangular liga- 

 ments, the lesser omentum, the fibrous capsule of the liver and the con- 

 nective tissue portion of the serosa. It also gives rise to the connective 

 tissue found within the liver. 



Development of the veins of the liver. As seen in Fig. 245, A, the liver 

 at once comes into close relation with the vitelline veins. The latter branch 

 about the ramifications of* the hepatic trabeculae producing sinusoids 

 (described on page 125). At first there are two vitelline veins, a right and 

 a left, one on either, side of the intestinal tract. They anastomose with 

 one another dorsal to the duodenum as shown in Fig. 247, A. Ventral to a 



more distal portion of the duodenum they fuse 

 and thus proceed to the yolk sac. By the 

 obliteration of the portions of these veins in- 

 dicated in Fig. 247, B, the portal vein is formed, 

 and its adult relations to the duodenum are ex- 

 plained. It receives the blood from the intes- 

 -s.m.v tines, stomach, spleen and pancreas, through 

 A B branches which develop later, and conveys it to 



FlG - 247 - the liver. It follows the hepatic duct and its 



The formation of the portal vein, 



P. v., from the right and left branches into the liver, where it is resolved into 



vitelline veins, r. v., and 1. v. ; 



:'*" ^S m'eSXfc' sinusoids. These unite anteriorly to form that 

 part of the vena cava inferior which passes 



from the liver to the right atrium of the heart. As may be seen in Fig. 

 245, this part of the vena cava is essentially a persistent portion of the vi- 

 telline veins. Three other veins connect with the vitelline sinusoids in the 

 liver, namely the right subcardinal vein which forms a large part of the 

 vena cava inferior, and the right and left umbilical veins. 



The distal portion of the v6na cava inferior is derived from the right 

 vein of a pair which pass up the back near the aorta; their position may 

 be understood since their anterior parts persist as the azygos and hemiazygos 

 veins of the adult. In the embryo these veins are prolonged posteriorly 

 (in part) as the right and left subcardinal veins, shown in the cross section, 

 Fig. 248. This figure indicates also that the liver fuses with the dorsal 

 wall of the abdominal cavity on the right side of the body (at x). No cor- 

 responding adhesion occurs on the left. After the fusion has taken place, 

 the right subcardinal vein anastomoses with the hepatic sinusoids, and all 

 of the blood from the limbs which it formerly took to the heart by way of 



