142 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



is the lesser peritoneal sac. In the liver to the left of the midline is the ductus venosus, sectioned 

 just at the point where it receives the left umbilical vein and a branch from the portal vein. 

 The ventral attachment of the liver later becomes the falciform ligament. 



Section through the Hepatic Diverticulum (Fig. 134). The section passes through 

 the pyloric end of the stomach and the duodenum near the attachment of the hepatic diverti- 

 culum. The great omentum of the stomach is larger than in the previous section and to its 

 right, in the plica venae cava?, lies the inferior vena cava. Ventral to the inferior vena cava 

 is a section of the portal vein. The ventral and dorsal lobes of the liver are now separate and 

 in the right ventral lobe is embedded the saccular end of the hepatic diverticulum, which forms 

 the gall bladder. To the right of the stomach, the diverticulum is sectioned again just as it 

 enters the duodenum. Ventrally the left umbilical vein is entering the left ventral lobe of the 

 liver. It is much larger than the right vein, which still courses in the body wall. On the 

 left side of the embryo the spinal nerve shows in addition to its dorsal and ventral rami a sympa- 

 thetic ramus, the fibers of which pass to a cluster of ganglion cells located dorso-lateral to the 



Post cardinal 

 vein 



Mesonephros 



L.Vitelline 

 vein 



Dorsal pancreas 

 Liver 



Inf. Vena cava 



R.vitelline or 

 portal vein 



Mesonephric 

 duct 



_ _ Duodenum 



Ventral pancreas* 



FIG. 135. Portion of a transverse section through the pancreatic anlages of a 10 mm. pig embryo. 



X 22.5. 



aorta. These cells form one of a pair of sympathetic ganglia and are derived from a spinal 

 ganglion. 



Section through the Pancreatic Anlages (Fig. 135). The lesser peritoneal sac just 

 above the level of this section has opened into the peritoneal cavity through the epiploic 

 foramen (of Winslow). The mesonephric ducts are now prominent ventrally in the mesonephroi. 

 The duct of the dorsal pancreas is sectioned tangentially at the point where it takes origin from 

 the duodenum. From the duct the lobulated gland may be traced dorsad in the mesentery. 

 To the right of the dorsal pancreatic duct is a section of the ventral pancreas, which may be 

 traced cephalad in the series to its origin from the hepatic diverticulum. Dorsal to the ventral 

 pancreas is a section of the portal vein. The inferior vena cava appears as a vertical slit in 

 the dorsal mesentery. 



Section through the Urogenital Sinus and the Lower Limb Buds (Fig. 136). 

 The figure shows only the caudal end of a section, in the dorsal portion of which the mesonephroi 

 were sectioned at the level of the subcardinal anastomosis. A portion of the mesentery is shown 

 with a section of the colon. In the body wall are veins which drain into the umbilical veins, 

 and on each side are the umbilical arteries, just entering the body from the umbilical cord. Be- 

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



