GLANDS. 437 



time of birth, scarcely any traces of them can be found. At the end of 

 the third month, the kidneys consist of seven or eight lobules, the future 

 pyramids ; their secreting ducts still terminate in the same canal, which 

 receives those of the Wolffian bodies and of the sexual organs. And 

 this opens with the rectum into a sort of cloaca, or sinus urogenitalis, 

 analogous to that which is permanent in the oviparous Vertebrata. 

 The kidneys are at this time covered by the supra-renal capsules, 

 which are very large ; about the sixth month, however, these have de- 

 creased, whilst the kidneys have increased, so that their proportional 

 weight is as 1 to 4|. At birth, the weight of the kidney is about three 

 times that of the supra-renal capsules, and they bear to the whole 

 body the proportion of 1 to 80 ; in the adult, however, they are no 

 more than 1 to 240. The Corpora Wolffiana are, when at their greatest 

 development, the most vascular parts of the body next to the liver ; 

 four or five branches from the aorta are distributed to each, and two 

 veins are returned from each to the vena cava. The upper veins and 

 their corresponding arteries are converted into the renal and emulgent 

 vessels ; and the lower, into the spermatic vessels. The lobulated appear- 

 ance of the kidney gradually disappears ; partly in consequence of the 

 condensation of the areolar tissue, which connects the different parts ; 

 and partly through the development of additional tubuli in the inter- 

 stices." 



It is only necessary to observe, in addition to the descrip- 

 tion of Dr. Carpenter, that, although the development of the 

 kidney commences near to the Wolffian body, it is yet not 

 formed out of it, but has an independent origin in its own 

 proper blastema or primordial matter. In its earliest condi- 

 tion in the Mammalia, it consists of tubes proceeding from 

 the hilus outwards towards the circumference in bundles ; 

 these tubes afterwards separate and become contorted, yet 

 all terminate in enlarged and vesicular extremities, the 

 Malpighian bodies. In the earliest state in which the kidney 

 can be examined, the caeca alone exist in connection with 

 short tubes ; the central or proximal extremities are free, 

 and not yet united to the ureter. This fact proves that the 

 kidney is not an involution of the genito-urinary mucous 

 membrane, but an independent formation, as is, probably, 

 every other gland. 



Such is a simple, concise, and, it is believed, in all essen- 

 tial particulars, a correct account of the normal tmatomy of 

 the kidney. 



