198 



THE UROGENITAL SYSTEM 



and into this wall grows a knot of arteries to form the glomerulus (embryos 

 of 5 to 7 mm.). The tubule, at first solid, hollows out and is lined with a low 

 columnar epithelium. The outer wall of the vesicle about the glomerulus is 

 Bowman's capsule, the two constituting a renal corpuscle of the mesonephros (Fig. 

 206 D) . In the human embryo the tubules do not branch or coil as in pig embryos, 

 consequently the mesonephros is relatively smaller. At 10 mm. about 35 



Mesonephric dtKt 



Anlage of ^ 



mesonephric tubule ' :;?'■"■.' 



Degenerating q 

 mesonephric corpuscle 

 Degenerating mesonephric. 

 corpuscle and tubule 



Tubule, 



Bowman's capsule 



Fig. 206. — Diagrams showing the differentia- 

 tion of the mesonephric tubules (modified after 

 Felix). L., lateral; M., median. 



Mesonephric tubule 



Glomerulus and Bowman's^ 

 capsule 



Mesonephric 

 duct 



Metanephros 



Ureter 

 Rectum 



Fig. 207. — Diagram showing the anlages 

 of the urinary organs in about 10 mm. human 

 embryos as seen from the left side (based on 

 reconstructions by Keibel and Felix). 



tubules are present in each mesonephros and the glomeruli are conspicuous 

 (Fig. 207) . Each tubule shows a distal secretory portion and a proximal collect- 

 ing part which connects with the duct (Fig. 208). 



The glomeruli form a single median column, the tubules are dorsal and the 

 duct is lateral in position. Ventro-lateral branches from the aorta supply the 

 glomeruli, while the posterior cardinal veins, dorsal in position, break up into a 

 network of sinusoids about the tubules (see Chapter IX). 



