138 



THE HUMAN SPECIES 



tinct lobes. When the lobes are partly united the surface of 

 the kidney becomes tuberculated, as in hyaena, ox and ele- 

 phant ; when the cortical substance of the lobes is completely 

 fused the surface of the kidney is quite smooth. If the lobes 

 coalesce to such an extent that the majority thereof or the en- 

 tire number are affected the result is a much smaller number of 

 papillae, indeed there is sometimes but one single papilla present, 

 as in the Marsupials, Edentata, Rodentia and certain of the Car- 

 nivora, e.g., the dog and the cat. 



FIG. 76. Section of human kidney FIG. 77. (i) Malpighian body of man. 

 (Ranke). a, renal papillae ; b, apex; A, B, C, Tubuli uriniferi ; magnified 



c, middle part ; d, cortical layer ; e, 300. (2) 3 epithelial cells from 



pelvis renalis ; f, ureter. convoluted canaliculi ; magnified 



350. (Kolliker, Gewebelehre.) 



A peculiarity shared by man with all the mammals is that 

 at first the ureters are embedded in the urachus section of the 

 allantois, from which the urinary bladder is gradually developed, 

 the process of the urachus towards the umbilicus and umbilical 

 cord becoming ultimately obliterated. The consequence is that 

 the bladder originally projecting far into the abdominal cavity 

 gradually retreats to' the pelvis. The size of the urinary bladder, 

 as well as its general structure, varies in the different mammals. 

 In the Bovidae it is highly convoluted, in the Carnivora smaller, 

 more muscular and almost circular. 



