THE DEVELOPMENT OF THE UROGENITAL SYSTEM. 397 



tubules, to form Henle's loop. The part between Henle's loop and the straight 

 tubule elongates and becomes convoluted to form the proximal part of a con- 

 voluted renal tubule (second convoluted tubule) . The part between the distal 

 end and Henle's loop elongates and becomes convoluted to form the distal part 

 of a convoluted renal tubule (first convoluted tubule) (Figs. 356 and 357). 



To avoid confusion it may be well to call attention to the fact that what has here been 

 called the proximal part of a convoluted tubule corresponds with what is usually described as 

 the second or distal convoluted tubule, and that the distal part of a convoluted tubule 

 corresponds with the first or proximal convoluted tubule. In histology the distal and proxi- 

 mal convoluted tubules are spoken of in relation to the renal corpuscle, but in development 

 it is more convenient to speak of the terminal part of a tubule as its distal part. 



Caudal 

 evagination 



Ureter 



FIG. 352. From a model of the primitive renal pelvis and the evaginations which form the cephalic, 

 central and caudal straight renal tubules of the first order. Human embryo of 4f months. 

 Compare with Fig. 350. Schreincr. 



A glomerulus develops in connection with the extreme distal end of a con- 

 voluted tubule or, in other words, with the distal loop of the S (p. 396). There 

 occurs here a further condensation of the mesenchyme, into which grows a 

 branch from the renal artery. This, as the afferent vessel of the ' glomerulus 

 breaks up into several arterioles, each of which gives rise to a tuft of capillaries. 

 These tufts are separated from one another by somewhat more mesenchymal 

 tissue than separates the capillaries within a tuft. The tufts with the asso- 

 ciated mesenchymal tissue constitute a glomerulus, and it is the mesenchymal 

 septa between the tufts that give to the glomerulus its characteristic lobulated 

 appearance. The capillaries of each tuft empty into an arteriole, and the 

 several arterioles unite to form the efferent vessel of the glomerulus, which passes 

 out along side of the afferent vessel. The renal tubule becomes flattened on the 

 side next the condensation of the mesenchyme, and as the glomerulus develops, 

 the epithelium of the tubule grows around it except at the point where the blood 



