HISTOLOGY 



the straight descending collecting tubule. From the capsule to the collect- 

 ing tubule no branches occur; and this extent of the tubule represents the 

 part derived from mesenchyma. The collecting tubules receive many 

 branches. Traced toward their outlet in the pelvis they become larger, 

 finally forming the papillary ducts. 



In the diagram (Fig. 310) the tubules are represented as much coarser than is actu- 

 ally the case. Their true proportions in the rabbit's kidney have been shown by Huber, 

 who, with extraordinary success, has isolated individual tubules, keeping them intact 

 from the capsule to the collecting tubule (Anat. Rec., 1911, vol. 5, pp. 187-194). They 

 are 20-30 mm. in length and less than o.i mm. in diameter. Huber's account of the 

 development of the kidney, from which Figs. 307-309 have been taken, is in the supple- 

 ment to the Amer. Journ. Anat., 1905, vol. 4. 



Surface Markings. Before studying sections of the kidney micro- 

 scopically, the small subdivisions of the organ which may be seen upon its 

 cut surface should be examined. They are shown in transverse section 

 in Fig. 311, but appear equally well when the kidney is divided length- 



cortex. 



Pars convoluta. Pars radiata. 



Pyramid 



(Medulla). 



Papilla. 



Renal column. 



FIG. 311. THE SURFACE MARKINGS OF THB HUMAN KIDNEY. (After Brodel.) 



wise. The ureter opens into the pelvis, which is prolonged into the cup- 

 like calyces, two of which are shown in Fig. 311. Each calyx receives 

 a nipple-like projection of the substance of the kidney, known as a renal 

 papilla. Sometimes two of them project into one calyx. They are soft, 

 dark red structures, and it does not appear on inspection that the grayish 

 lining of the calyx is reflected over their outer surface; this is seen in sec- 

 tions. Toward the apex of each papilla there are from 15 to 20 foramina, 

 which are the orifices of as many papillary ducts; through them the urine 

 enters the calyx. The foramina are barely visible without magnifica- 

 tion. Each papilla forms the apex of a renal (or Malpighian) pyramid, 

 described by Malpighi (1666) in his treatise " on the structure of the vis- 

 cera," which gave the first account of various almost microscopic "corpus- 



