226 



ANATOMY or VERTEBRATES. 



CHAPTEK XXI. 



URINARY SYSTEM OF BIRDS. 



108 



,j^^~)0. 



§ 160. Kidneys of Birds. — The urinary excretion is early pro- 

 yided for in the bird : about the third day of incubation a series 

 of short parallel caecal tubes, fig. 108, c, are developed in the 

 blastema beneath the vertebral column, and pass transversely to 

 a longitudinal canal, ib. d, which conveys the excretion to the 

 cloaca. These are the primordial or transitory kidneys. Behind 

 them subsequently appear the secondary or persistent kidneys, ib. 

 «, together with the genital glands, ib. e, and adrenals, ib. f. The 

 proper ducts of the kidneys, or ureters, ib. 

 h, soon follow the appearance of the true 

 renal tissue, and as this proceeds in its de- 

 velopement, the primordial glands disappear, 

 or yield up their duct and a remnant of their 

 tissue to form the epididymis and vas deferens 

 in the male. 



In the mature bird the urinary system 

 consists of the kidneys, ureters, and a more 

 or less incomplete urinary receptacle. 



As in Reptiles the kidney is distinguished 

 from that of the Mammal by the homogeneity 

 of its substance, which is not divided into a 

 cortical and medullary part, and by the tubuli 

 uriniferi extending to the surface of the gland 

 testes of an embryo Bird, mag- thcrc to form bv rcitcratcd unious the ureter, 



nifled. Lxxiv. ... . . . 



and not terminating m a cavity or pelvis in 

 the interior of the kidney, from which the ureter commenceSo 



The kidneys, fig. 85, x, are two in number, of an elongated 

 form, commencing immediately below the lungs, and extending 

 along the sides of the spine as far as the termination of the rectum ; 

 in which course they are impacted in, and as it were moulded to, 

 the cavities and depressions of the j)elvis. From this fixed con- 

 dition it results that they are generally symmetrical in position, 

 not placed one higher than the other, as in the Mammalia. The 

 posterior surface of the kidney presents inequalities corresponding 



I 



m 



Kidneys, 'Wolfflan bodies, and 



