TRANSVERSE SECTIONS OE A TEN MM. PIG EMBRYO 



135 



nephroi were sectioned at the level of the suhcardinal anastomosis. A portion of the : 

 is shown with a section of the colon. In the body wall are veins which drain into the umbihcal 

 veins, and on each side are the umbilical arteries, just entering the body from the umbihcal 

 cord. Between them, in sections cranial to this, the allantoic stalk is located. Here it has 

 opened into the crescentic urogenital sinus. Dorsal to the urogenital sinus (dorsal now being 



Dorsal aori 1 

 Inferior vena cava. 



R. vitelline or portal vcin-i 

 Mesonephric duel' 

 Ventral pancreas 



I I cardinal vein 



Mesonephros 



L vitelline vein 

 Dorsal pancreas 

 Liver 



Duodenum 



Fig. 140. — Portion of a transverse section through the pancreatic anlages of a 10 mm. pig embryo. 



X 22.5. 



at the bottom of the figure owing to the curvature of the caudal region) is a section of the 

 rectum, separated from the sinus by a curved prolongation of the coelom. From the ends of 

 the urogenital sinus, as we trace cephalad in the embryo {downward in the series), are given 

 off the mesonephric ducts. 



Mesentery' 



Lower limb hud- 



Mesonephric du 



Vein in body wall 



L. umbilical artery 



Allantois and 

 urogenital sinus 



Notochord 



Rcciiim 



■Spinal cord 



Fig. 141. — Transverse section through the urogenital sinus and rectum of a 10 mm. pig embryo. X 22.5. 



Section through the Mesonephric Ducts at the Opening of the Ureter (Fig. 142). 

 — The section cuts through both lower limb buds near their middle. Mesial to their besas 

 are the umbilical arteries, which lie lateral to the mesonephric ducts. From the dorsal wall of 

 the left mesonephric duct is given off the ureter or duct of the metanephros. Tracing the sec- 

 tions down in the series, both ureters appear as minute tubes in transverse section. They 



