Io8 THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



into the pleuro-peritoneal cavities are ridges of mesencyhma covered by splanchnic mesoderin 

 in which the lungs develop as lateral buds from the. caudal end of the trachea. The right 

 lung bud is shown in the figure. Between the esophagus and the lung is a crescent-shaped 

 cavity, the cranial end of the lesser peritoneal sac. 



Transverse Section through the Stomach (Fig. 111).— The section passes through 

 the upper limb buds and just caudal to the point at which the descending aortae unite to form 

 the median dorsal aorta. As the liver develops in early stages, it comes into relation with the 

 plica vence cava: along the dorsal body wall at the right side of the dorsal mesogastrium. The 

 space between the liver and phca to the right, and the stomach and its omenta to the left, is 

 a caudal continuation of the lesser peritoneal sac. The dorsal wall of the stomach is rotated 

 to the left, its ventral wall to the right. The hver shows a pair of dorsal lobes and contains 

 large blood spaces and networks of sinusoids lined with eridothehum. Ventral to the Hver, 

 the tips of the ventricles are seen. 



cord 

 inal nerve 



Peritoneal nnil\ 

 Lesser 1 



Common hepulic i in 

 {R. vitelline) 



R. ventral lobe Ii i 



R, ventrul 



Post, cardinal vein 

 Upper limb hid 

 Stomach 



~ L. ventral lobe of liver 



ventricle 



Fig. 111. — Transverse section through the stomach of a 6 mm. pig embryo. X 26.5. 



Transverse Section through the Hepatic Diverticulum (Fig. 112). — The upper 

 limb buds are prominent in this section. The mesonephric folds show the tubules and glom- 

 eruli of the mesonephroi and the posterior cardinal veins are connected with the mesonephric 

 sinusoids. From the dorsal attachment of the liver there is continued down into this section 

 a ridge on the dorsal body wall just to the right (left in figure) of the mesentery. In this ridge 

 lies a small vein which connects cranially with the liver sinusoids, caudally with the right 

 subcardinal vein. As it later forms a portion of the inferior vena cava, the ridge in which it 

 lies is termed the plica venoe cavcE or caval mesentery. The right dorsal lobe of the liver contains 

 a large blood space into which the portal vein opens. The duodenum is ventral to the position 

 occupied by the stomach in the previous section. There is given off from it ventrad and to 

 the right the hepatic diverticulum. In the sections higher up small ducts from the liver tra- 

 beculsE may be traced into connection with it. In the left ventral lobe of the liver, a large 

 blood space indicates the position of the left umbilical vein on its way to the ductus venosus. 



Transverse Section through the Dorsal Pancreas (Fig. 113). — At this level the 

 upper limb buds still show; the mesonephroi are larger and marked by their large glomeruli. 



