38 



Development and Shape of Urinifcroiis Tubules 



this I have followed him), an upper S-curve, an S middle piece and a lower S-curve 

 The upper S-curve passes without definite boundary into the S-middle piece. The lower 

 S-curve grows upward toward the lateral bend of the upper S-curve ; in this wav 

 there is formed between it and the .S-middle piece on the one hand and the concavit.v 

 of the lower S-curve on the other hand, a curved cleft, into which vascularized 

 mesenchyme grows and forms the aulage of the glomerulus. From his reconstruc- 

 tions, he was able to see that the lower S-curve is in reality not a tubule, but is spread 





Fig. 7. A portion of a longitudinal section of the kidney of a human 

 embryo measuring 6.5 cm. in length (No. 11), showing a primary columna 

 Bertini, which extends from the capsule to near the pelvis of the kidney. 

 X 80. Pcb, primary columna Bertini; c, capsule; pe, epithelium of pelvis; d, 

 end branches of collecting tubules. 



out, beginning with the place where the S-middle piece passes into it " into a thin, 

 spherically curved and downward bellying structure with a sharp border, having the 

 torm of a triangle with rounded angles : the base of this triangle represents the up- 

 curved, blind ending of the S-shaped tubule, as seen in sections. Over the middle 

 of this structure with upward facing concavitv is found just a little above it the 

 junction of the upper S-curve with the S-middle piece." The lower curve of the S, 

 which is not solid but hollow has therefore the shape of an oyster shell (" Muschel- 

 schale") and. to continue the comparison, we mav sav with one having a deeper 

 concavity with edges rolled in somewhat, the more' fully developed the structure is. 



