THE KIDNEYS. 



725 



Fig. 367. Vertical Section of Kidney, 



surface of the kidney, forming a layer about two lines in thickness, where it covers 

 the pyramids, and sends numerous prolongations inwards, towards the sinus between 

 the pyramids. 



The cortical substance is soft, reddish, 

 granular, easily lacerated, and contains nu- 

 merous small red bodies disseminated through 

 it in every part, excepting towards the free 

 surface. These are the Malpighian bodies. 

 The cortical substance is composed of a mass 

 of convoluted tubuli uriniferi, bloodvessels, 

 lymphatics, and nerves, connected together 

 by a firm, transparent, granular substance, 

 which contains small granular cells. 



The medullary substance consists of pale, 

 reddish-colored, conical masses, the pyra- 

 mids of Malpiglii, varying in number from 

 eight to eighteen; their bases are directed 

 towards the circumference of the organ, 

 whilst their apices, which are free from the 

 cortical substance, converge towards the 

 sinus, and terminate in smooth, rounded ex- 

 tremities, called the papillse (mammillae) of 

 the kidney. Sometimes, two of the masses 

 are joined, and have between them only one 

 papilla. The kidney is thus seen to consist 

 of a number of conical-shaped masses, each 

 inclosed, excepting at the apex, by an invest- 

 ment of the cortical substance; these repre- 

 sent the separate lobules of which the human 

 kidney in the foetus consists, a condition 

 observed permanently in the kidneys of many of the lower animals. - As the 

 human kidney becomes developed, the adjacent lobules coalesce, so as to form a 

 single gland, the surface of which, even in the adult, occasionally presents faint 

 traces of a lobular subdivision. 



The medullary substance is denser in structure than the cortical, darker in color, 

 and presents a striated appearance, from being composed of a number of minute 

 diverging tubes (tubuli uriniferi}. The tubuli uriniferi commence at the apices of 

 the cones by small orifices, which vary from 

 Fi7 to 2 ^ff of an inch; as they pass up in 

 the medullary substance, towards the peri- 

 phery, they pursue a diverging course, di- 

 viding and subdividing at very acute angles, 

 until they reach the cortical substance, when 

 they become convoluted, anastomose freely 

 with each other, and retain the same diameter. 

 The number of orifices on the entire surface 

 of a single papilla is, according to Huschke, 

 about a thousand ; from four to five hundred 

 large, and as many smaller ones. The tubuli 

 uriniferi are formed of a transparent homo- 

 geneous basement membrane, lined by sphe- 

 roidal epithelium, which occupies about two- 

 thirds of the diameter of the tube. The 

 tubes are separated from one another, in the 



medullury cones, by capillary vessels, which form oblong meshes parallel with the 

 tubuli, and by an intermediate parenchymatous substance composed of cells. 



As soon as the tubuli uriniferi enter the cortical substance (fig. 368), they 



Fig. 368. Minute Structure of Kidney. 



