THE KIDNEYS SECRETION OF URINE. 



[Fig. 241. 



633 



13 1 



Represents the half of a Kidney di- 

 vided vertically, and with its arteries 

 injected ; the matter has also passed 

 into the excretory ducts; 1, 2, branches 

 of the emulgent artery ; 3, 3, hilum re- 

 nale ; 4, 4, cortical substance, as essen- 

 tially formed by the capillary termina- 

 tions of the vessels of the kidney ; 5, 

 medullary or tubular portion.] 



A view of half a Kidney divided vertically from its con- 

 vex to its concave edge ; one of its extremities is perfect; 

 1, 1, the lobes which form the kidney ; 2, 2, the lines of se- 

 paration of these lobes; 3, the cortical substance; 4, 5. the 

 pyramids of Malpighi ; 6, the hilum renale split up and 

 cleared of its vessels ; 7, 7, points to the tubes of Bellini ; 

 8, one of the papillae ; 9, 10, two other papillte, uncut, but 

 Jeprivedof the calices that surrounded them; 11, one of the 

 foveolae in the papilla; 12,12, the vascular circle sur- 

 rounding the papillce ; 13, circumference of the tubular 

 portion ; 14, external surface of the kidney ; 15, the por- 

 tion of its external surface on a line with its fissure.] 



tion, vary greatly in different species. The uriniferous tubes are connected 

 together by a very loose areolar web. The structure of the gland in Reptiles 

 appears to be essentially the same ; its form, however, varies considerably 

 in the different tribes, being greatly prolonged in the Serpents, and abbreviated 

 in the Tortoises. In the Crocodile, the distinction between the cortical and 

 medullary portion begins to show itself; the tubes being nearly straight where 

 they issue from the ureter, and being convoluted near the surface only of the 

 lobes. The Corpora Malpighiana ( 839, 6), however, where they exist in this 

 class, are scattered through the whole substance ; not being confined, as in 

 higher animals, to the cortical portion. In Birds, the urinary tubes, forming 

 the several clusters, are more closely united together; they frequently ramify 

 to a considerable degree. In the Mammalia, as in Man, there is an evident 

 distinction between the straight and the convoluted portions of the system of 

 tubes ; the former character is seen in the medullary substance ; the latter in 

 the cortical. In nearly all below the Mammalia, the kidneys present exter- 

 nally a lobulated aspect ; resulting from the want of union between the differ- 

 ent bundles of tubes, which arise from separate parts of the ureter. In the 

 kidney of the Mammalia, however, the ureter dilates into a capacious recep- 

 tacle, towards which the several bundles of uriniferous tubes converge, so 

 that they open into it in close proximity with each other; and the lobules 

 formed by these bundles are so closely brought together, that no appearance 

 of a division presents itself, until a section of the gland is made. Among 

 some Mammalia, however, the lower form is still retained ; and it is presented 

 in the Human species also, at an early period of its foetal development. 



839. The following is an account of the structure of the Kidney, according 

 to the most recent investigations.* 



* See Bowman in Philosophical Transactions, 1842; also Gerlach, in Miiller's Archiv., 

 Heft 4, 1845, and in Banking's Abstract, vol. iii. p. 307. 



