CHAP. XVII.] 



ELIMINATION. 



205 



The structure of the kidney. The kidney is a secreting gland, 

 constructed upon the general plan of a compound secreting 

 ' gland, but possessing special features peculiar to itself. If we 

 cut a kidney in two lengthwise, it is seen that the upper end of 

 the ureter expands into a basin-like cavity, into which the solid 

 portion of the kidney projects in conical-shaped masses. This 

 dilated cavity of the ureter is called the pelvis or basin of the 

 kidney, and this 

 pelvis is irregu- 

 larly subdivided 

 into smaller, cup- 

 like cavities, called 

 calices, which re- 

 ceive the pointed 

 projections of the 

 kidney substance. 



The substance of 

 the kidney is read- 

 ily seen by the 

 naked eye to con- 

 sist of two distinct 

 parts : an outer, 

 darker, and more 

 solid portion, called 

 the cortex (bark), 

 and an inner, lighter 

 striated portion, 

 called the medulla 



(marrow), which IS dulla; py> pap in a O f pyramidal section projecting into 

 not a solid mass but one of the calices of pelvis; R.A, renal artery; R. V, 



-, j . renal vein ; U, ureter, 



more or less dis- 

 tinctly divided into pyramidal-shaped sections. The pointed 

 projections orpapillce of the pyramids are received by the irregu- 

 larly disposed cup-like cavities of the pelvis. The bulk of the 

 kidney substance, both in the cortex and medulla, is composed 

 of little tubes or tubules, closely packed together, having only 

 just so much connective tissue as is sufficient to carry a large 

 supply of blood-vessels and a certain number of lymphatics and 

 nerves. The different appearance of cortex and medulla is due 

 to the shape and arrangement of tubules and blood-vessels. 



FIG. 123. SECTION THROUGH THE KIDNEY SHOW- 

 ING THE MEDULLARY AND CORTICAL PORTIONS, AND 

 THE BEGINNING OF THE URETER, ct, cortex; M, me- 



