THE SECONDARY KIDNEYS. 413 



are occupied by vascular coils (glomeruli). The further 

 growth of these tubes results in the compact secondary 

 kidney, which, in Man and most higher Mammals, acquires 

 the well-known bean-like form ; in the lower Mammalia, 

 in Birds and in Reptiles, on the other hand, it is separated 

 into several lobes. The lower, or posterior part of the 

 permanent kidney duct retains the form of a simple canal, 

 widens, and thus forms the permanent urine duct (ureter). 

 At first this canal, yet united with the last section of the 

 primitive kidney duct, discharges into the cloaca; at a 

 later period, it separates from the primitive kidney duct, 

 and yet later from the rectum, and then it discharges into 

 the permanent urinary bladder (vesica urinaria). The 

 latter originates from the posterior, or lower part of the 

 stalk of the allantois (urachus), which widens and becomes 

 spindle-shaped before opening into the cloaca. The anterior, 

 or upper part of the allantois-stalk, which -passes in the 

 abdominal wall of the embryo to the navel, afterwards 

 disappears, a useless cord-shaped remnant alone remaining 

 as a rudimentary organ : this is the single urinary-bladder 

 navel-cord (ligamentum vesico-umbilicale medium). On 

 the right and left of this, in the adult Man. there are two 

 other rudimentary organs : the lateral urinary-bladder navel- 

 cords (ligamenta vesrlco-umbilicalia lateralia). These are 

 the obsolete cord-like remnant of the former navel-arteries 

 (arterice umbilicales, vol. i. p. 400 ; Fig. 326, a). 



Although in Man, as in all other Ainnion Animals, the 

 primitive kidneys are thus very early displaced by the 

 secondary kidneys, and although the latter alone afterwards 

 act as urinary organs, the former are not, however, alto- 

 gether discarded. Indeed, the primitive kidney ducts acquire- 



