368 



EXCRETION 



M ^ 



opening. Unlike the skin, the action of these bodies is 

 purely excretory, and to them is due the purification of 

 the blood. 



Structure of the kidney. — The ordinary lamb's kidney 

 which may be obtained from the butcher serves well to 

 demonstrate the structm-e of this important organ. 



Removing the fat from the outside we find the reddish- 

 brown kidney within, still surrounded with a trans- 

 parent membrane or capsule. This membranous capsule is 



called the renal capsule. 

 Remove this and we 

 have the kidney. 



Viewed from the out- 

 side it shows a bean- 

 shaped outline, being 

 convex on one side and 

 concave on the other. 

 In the depression on the 

 concave side may be 

 made out the connect- 

 ing renal vein and 

 artery and the ureter 

 at the point where they 

 enter the body of the 

 kidney. If we cut the 

 kidney lengthwise the 

 cut surface shows the 

 following areas (see 

 Fig. 169). As it enters the kidney the narrow ureter 

 is seen to widen into a cavity called the pelvis. From this 

 pelvis extend branches forming what are called calices. 

 The solid portions show two layers. The outer is caUed 



WA. 



Fig. 169 — ivredian longitudinal section of a 

 kidney; Ct, cortex; M, medulla; P, pelvis- 

 U, ureter; RA^ renal artery; P(/, pyramids 

 of Malpighi, 



