THE MESONEPHROS 



199 



tubule enlarges, becomes thin walled, 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. 2o6D). In the 

 human embryo the tubules do not branch or coil as in pig embryos, con- 

 sequently the mesonephros is relatively smaller. At 10 mm., about 35 



Mesonephric duct 



Anlageof 



mesonephric tubule < -.>": 



Degenerating 

 mesonephric corpuscle 

 Degenerating mesonephric 

 corpuscle and tubule 



Tubule 



Bowman's capsule 



Developing mesonephric 



corpuscle 

 Urogenital sinus 



Glomerulus and Bowman's, 

 capsule 



Mesonephric 

 duct 



Metanephros 



FIG. 206. Diagrams showing the FIG. 207. Diagram showing the anlages 



differentiation of the mesonephric tubules of the urinary organs in about 10 mm. human 



(modified after Felix). L. lateral; M, embryos, as seen from the left side (based on 



median. reconstructions by Keibel and Felix). 



'L- 



tubules are present in each mesonephros and the glomeruli are conspicuous 

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

 collecting 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, 

 (Fig. 323), while the posterior cardinal veins (Fig. 72), dorsal in position, 

 break up into a network of sinusoids about the tubules (see Chapter IX). 



