THE ABDOMEN 831 



sents the primitive ureter, and its cephalic enlargement corresponds to the 

 primitive renal pelvis. The pelvic enlargement furnishes secondary diver- 

 ticula, which grow into the metanephric blastema, and represent the calices. 

 These, in turn, give off tubular branches, which, becoming extended and 

 subdivided, give rise to the excretory tubules of the medullary part of the 



kidney. j v 1 



The comphcated system of tubules in the cortical part, beyond the col- 

 lecting or excretory tubules — namely, the secretory tubules — are developed 

 from the metanephric blastema, which surrounds the enlarged cephahc 

 extremity of the renal diverticulum. The tissue of this blastema becomes 

 differentiated into two zones — outer and inner. The mesodermic tissue of 

 the outer zone furnishes the connective-tissue stroma and capsule of the 

 kidney as well as the columns of Bertini. 



Suprarenal Bodies 



HuUerian Duct f f\j | y*>j /v^ fikrr-r V,Mullerian Duct 



. Kidneys 



.Rudiments of Sex-Organs 



Wolffian Body \3^^^r{7 k^r^CM^&J— Wolffian Body 



I. Intestine 

 Wolffian Duct ..\2^S^^)I| ~ l\lfS^«K<^ ^°'®*° ^"*^' 



Mullerian Duct 



Genital Cord 



Uro-genital Sinus 



Cloa'.-a 



Fig. 360. — ^The Wolffian Bodies : Wolffian and Mullerlan Ducts, and 

 Contiguous Parts (Allen Thomson). 



The mesodermic tissue of the inner zone gives rise to solid outgrowths, which 

 at a later period become hollow and separated from the inner zone. These 

 outgrowths are called the renal vesicles. Each vesicle becomes elongated, 

 and forms an S-shaped tubule. One end of the S becomes connected with 

 the contiguous collecting tubule, into which it opens. The other end pertains 

 to a Malpighian corpuscle. 



Within the lower loop of the S a collection of mesenchyme appears, and 

 within this a glomerulus is developed. This glomerulus invaginates a portion 

 of the upper wall of the lower limb of the S. and the part thus invaginated 

 forms Bowman's capsule. The remainder of the lower limb represents the 

 commencement of the proximal convoluted tubule. As the S tubule elongates 

 it forms several curves, and thus gives rise to ( i ) the remainder of the proximal 

 convoluted tubule, (2) the spiral tubule, (3) Henles looped tubule, (4) the 

 irregular, or zigzag tubule, (5) the second convoluted tubule, and (6) the 

 junctional tubule. 



