534 



ANATOMY OF VERTEBRATES. 



352 



Lampreys * a continuous narrow elongated gland, which extends in 

 their young or Ammocete condition throughout the abdomen, but in 

 the full-grown fish (PetromyzoTi) along the posterior two thirds : in 



both being confined to the 

 dorsal part of the cavity, 

 fig. 354, g. The ureters, 

 ib. c, open into the short 

 canal leading to the pa- 

 pillary production of the 

 peritoneal outlets close 

 to the anus. 2 



In most Osseous Fishes 

 the kidneys are long and 

 narrow, and extend 

 through the whole or a 



o 



great part of the dorsal 

 region of the abdomen, 



o 



firmly attached to the 

 vertebral column ; they 

 are usually broadest and 

 thickest anteriorly , where 

 they sometimes present 

 a lobulated surface ; they 

 contract, approximate, 

 and frequently blend to- 

 gether as they extend 

 backwards ( Cyclopterus) ; 

 sometimes penetrating 

 the haemal canal in the 

 tail. In the Gymnotus 

 the kidneys are distinct 

 and thickest at their pos- 

 terior ends, as they are 

 in the Gurnard, fig. 379, 

 k, and in most Sharks. 

 The kidneys have not 

 a well-defined capsule 

 in Osseous Fishes, but 

 their ventral surface is immediately covered by an aponeurotic 

 membrane, against which the peritoneum, and the air-bladder 

 when present, are applied. The renal tissue is soft and spongy, 



1 In Petromyzon marinus the diameter of the tubuli urinifcri is n-^th of an inch, that 

 of the capillaries of the kidneys being j^th of an inch. 2 xx. iv. pi. 56, fig. 1, e. 



Viscera of male Shark, showing kidneys, n, in situ 



