TRANSVERSE SECTIONS OF A TEN MM. PIG EMBRYO 



141 



at this stage. The large vein penetrating the septum transversum from the liver to the heart, 

 is the proximal portion of the inferior vena cava, originally the right vitelline vein. Ventral 

 to the bronchi may be seen sections of the pulmonary veins. 



Section through Lung Buds Cranial to Stomach (Fig. 132).— The lungs are 

 sectioned through their caudal ends and the esophagus is just beginning to dilate into the 

 stomach. On either side of the circular dorsal aorta are the mesonephroi. The pleural cavities 

 now communicate freely on both sides with the peritoneal cavity. A section of the lesser 

 peritoneal sac appears as a crescent-shaped slit to the right of the esophagus. In the right 

 dorsal lobe of the liver is located the inferior vena cava. Near the median line ventral to the 

 lesser sac is the large ductus venosus. 



Notachord 

 Mesaneph, 



Plica, venae 

 cavae 



Inf. vena cava. 



Lesser peritoneal 

 Sac 



Portal vein 



Hepatic 

 diverticulum 



R. Umbilical, 

 vein 



Spinal cord 



Sympathetic 

 ramus 



Dorsal aorta. 



Dorsal 

 mesogastrium 



Mesonephric 

 'duct 



Stomach 



Ventral lobe 

 Liver 



LMmbilical 

 Vein 



Fig. 134. — Transverse section through the hepatic diverticulum of a 10 mm. pig embryo. 



X 22.5. 



Section through the Stomach and Liver (Fig. 133;. — Prominent in the body 

 cavity are the mesonephroi and liver lobes. The mesonephroi show sections of coiled tubules 

 lined with cuboidal epithelium. The glomeruli, or renal corpuscles, are median in position 

 and develop as knots of small arteries which grow into the ends of the tubules. The thickened 

 epithelium along the median and ventral surface of the mesonephros is the anlage of the genital 

 gland. The body wall is thin and lined with mesothelium continuous with that which covers 

 the mesenteries and organs. The mesothelial layer becomes the epithelium of the adult peri- 

 toneum, mesenteries and serous layer of the viscera. The stomach lies on the left side and is 

 attached dorsally by the greater omentum, ventrally to the liver by the lesser omentum. The 

 right dorsal lobe of the liver is attached dorsally to the right of the great omentum. In the liver 

 ventral to this attachment courses the inferior vena cava and the attachment forms the plica 

 vence cava. Between the attachments of the stomach and liver, and to the right of the stomach, 



