136 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



soon dilate to form the pelvis of the kidney at the level of Fig. 143. Note the undifferentiated 

 mesenchyme of the lower limb buds and their thickened ectodermal tips. 



Lower limb bud 

 R. umbilical arlcry 



Caudal limb of intestine 



*/ 'Mesonephric duct 

 C I tier 



Notochord 



Spiiui cord 



Fig. 142.— Transverse section of a 10 mm. embryo passing through the lower limb buds at the level of 

 the openings of the ureters into the mesonephric ducts. X 22.5. 



Section through the Metanephroi and Umbilical Arteries (Fig. 143).— The sec- 

 tion passes caudal to the mesonephric ducts which curve along the ventral surfaces of the 



Mesentery 



R. umbilical artery 

 Vein 



Ccelom 



Anlage of metanephros 



i\oloL hard 



Fig. 143. — Transverse section through the anlages of the metanephroi in a 10 mm. pig embryo. X 22.5. 



mesonephroi (Fig. 124). The umbilical arteries course lateral to the metanephroi which con- 

 sist merely of the thickened epithelium of the pelvis surrounded by a layer of condensed 

 mesenchyma, the nephrogenic tissue. 



