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. 2O6.D). 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 



Anlage of 



mesoncphric tulnilf 



Degenerating 

 mesonephric corpuscle 

 Degenerating mesonephrk 

 corpuscle and tubule 



M 



Mesonephric tubule 



Glomerulus and Bowman's 

 capsule 



Developing mesonephric 

 corpuscle 



Urogenital sinus 



Bowman's capsule 



Mesonephrk 

 duct 



Metanephros 



Ureter 

 Kectum 



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). 



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). 



