162 PHYSIOLOGY 



the point or edge of such 1 . In some there is only one mammilla, and 

 one infundihiilum, as in the lion tribe 2 ; in others there are a great many 

 mammillae and infundibula, as in the bonassns 3 . 



Loose ' Notes and Queries ' on the Kidney. 



The kidneys of all viviparous animals are much higher than those of 

 the viviparous < ex ovo,' or of the oviparous animals. Why so, is perhaps 

 not so easily accounted for, excepting it be to allow of more room for 

 the growth of the uterus. The kidneys in the two last are in what may 

 be called the pelvis, and the urethra, in them, enter the common passage 

 of the oviduct and rectum. 



Why do the ductus urinarii of the kidneys enter the pelvis on a convex 

 surface ? This may perhaps be to prevent a regurgitation back into the 

 blood ; as we see in the liver from a stone in the ducts 4 . 



Of Parts ivhose uses are not known. 



The capsula rents is a wrong name for those [suprarenal] bodies, as 

 they are not attached to the kidneys in all animals : in the lizard 

 they are placed between the testicle and epididymis. 



1 [Hunt. Preps. Nos. 1219, 1242.] - [lb. No. 1219.] 



3 [lb. No. 1258.] 



4 [This query could only relate to the higher animals, to which, as Hunter has 

 just shown, the ' convex surface ' or mammilla is peculiar. In all oviparous Verte- 

 brata the ' ductus urinarii ' are directly continuous with the ureter, of which they 

 are indeed ramifications ; and, among mammalia, the solipeds and some other odd- 

 toed hoofed beasts {Tapir, Rhinoceros) have the tubuli terminating on a concave 

 sm'face, and can be injected from the pelvis. Nevertheless the structure of the 

 mamniillre in other mammals seems intended to prevent regurgitation. Does the 

 disposition of the renal ducts in the Ovipara depend on the absence of constriction or 

 resistance at the end of the ureter, which is so placed as to allow of a ready and 

 constant discharge of the urinary secretion ? Does the absence of a urinary bladder 

 permit the superabun dance of earthy salts which characterizes the urine in these 

 classes, there being here no intermediate cavity or receptacle in which that matter 

 can accumulate to form a calculus ? It is evidently at variance with the structure 

 of the bird that it should be encumbered with an accumulated excretion, and conse- 

 quently it is in the ostrich and similar birds without the powers of flight, that the 

 convenience of a urinary receptacle is met with. This is, however, less perfectly 

 adapted to that end than in mammals. In the cold-blooded Ovipara a greater or 

 less proportion of the allantois remains. The accumulation of fluid contents in this 

 cavity can be of little physical consequence to animals which never raise their bodies 

 from the earth ; and are in general characterized by the sluggishness of their motions. 

 The bladder, however, appears in these to serve other purposes than that of a 

 urinary receptacle ; if it ever be filled with mere urine at all. (Tie up the ureters in a 

 frog or tortoise, and see if the urinary bladder becomes empty, also what kind of 

 urine accumulates in the constricted duct. Is it from the possibility of regurgitation 

 into the tubuli, that a horse stands still, and allows nothing to interfere with the 

 evacuation of the bladder in staling ?)] 



