37° 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



corresponding to the diverticula given off from the apex of the 

 ureter, each lobule having its own duct. This condition is retained 

 in adult elephants, some ungulates, carnivores (fig. 393) and primates, 

 and especially in the aquatic species (whales, seals), the lobules being 

 most numerous (200+) in some whales. In all other species the 

 ducts fuse and the lobules unite later into a compact mass lying in the 

 lumbar region near the last rib. 



Each kidney has a peculiar shape (giving rise to the adjective 

 reniform), convex on the lateral, concave on the medial side, the con- 



FiG. 394. — Model of cloacal region of human embryo, 6.5 mm. long, after Kelbel; 

 a, allantois; c, cloaca; cm, cloacal membrane; k, outgrowth to form kidney and ureter; 

 r, rectum; u, where bladder will develop; los, Wolffian duct. 



cavity being the Mum, from which the ureter arises and where the 

 renal artery and vein connect with the kidney. Except in Echidna, 

 there is a cavity, the pelvis of the kidney just inside the hilum, into 

 which one or several papillse project from the opposite wall, each 

 bearing the openings of numerous collecting tubules (p. 345). In 

 section the kidney shows two different textures, even to the naked eye. 

 The outer cortex appears granular, because there are collected the 

 Malpighian bodies and the convoluted tubules, while the inner 



