540 



ANATOMY OF VERTEBRATES. 



the plane, midway between these surfaces, are the similarly 

 disposed branches of the renal artery, a, and renal vein, v. The 

 material of the urinary excretion thrown by the epithelial cells or 

 bags from the inner surface into the cavity of the uriniferous 



tubules, t, is derived from 

 the rich venous plexus, p, 

 everywhere in contact with 

 their outer surface : the sero- 

 sity exuded from the dilated 

 arterial plexus in the Malpi- 

 ghian capsule, propelled by 

 the ciliary action, dilutes and 

 washes out the excretion 

 from the tubuli, whence it is 

 conveyed by the superficial 

 branches of the ureters to 

 the trunk, or ureter, com- 

 mon to the several renules, 

 and, by the ureters, is dis- 

 charged into the cloaca. 1 

 There is no urinary or allan- 

 toid bladder in Serpents. 



The kidneys in Lacertians, 

 fig. 301, k, fig. 332, are 

 shorter, broader, and less 

 subdivided than in Serpents ; 

 situated close to the verte- 

 bral bodies at the hinder part of the abdominal cavity ; they 

 are usually pointed at their forepart ( Cyclodus). In the Iguana 

 they are of an oblong, subdepressed form : their structure is 

 essentially that above described in the Boa. The ureter runs 

 superficially, as it collects its tributaries, along the free or ventral 

 surface of the kidney, and terminates in a slight eminence, papilla or 

 ridge, close to the genital orifice, in the urogenital compartment 

 of the cloaca, behind or dorsad of the anus. Anterior to, or sternad 

 of, the terminal orifice of the rectum, is that of the urinary or 

 allantoid bladder, of large size in the Iguana. In this reptile 

 Hunter found the bladder e filled with a white fluid,' and ' there 

 were small calculi in it.' 2 In the same reptile he records the pre- 

 sence of 'one brown calculus in each ureter, almost filling the 

 duct.' 3 



1 The ingenious and lucid explanation of the functions of the minuto structures 

 given by their discoverer, Mr. Bowman, in cxxxvu. 



2 ccxxxvi. vol. ii. p. 367. 3 Ibid. 



Tlan of disposition of blood-vessels and tubuli in the 

 renule of Boa. cxxxvu. 



