THE EXCRETORY AND REPRODUCTIVE 



SYSTEMS 



As explained in the last section, a portion of the waste prod- 

 ucts produced by the activity of the cells of the body is passed 

 off through the lungs, but some other outlet must be provided 

 for the excretions that are not in the form of gases. These 

 liquid excretions, containing various salts and urea, pass off 

 through the kidneys and the glands of the skin. 



The latter are of two kinds, sudoriferous or sweat glands, and 

 sebaceous or oil glands, with ducts opening into the hair follicles 

 near the surface. The sweat glands lie deeper than the seba- 

 ceous glands. The former are subcutaneous and consist of a 

 more or less coiled tube with a straight duct opening on the 

 surface. They are most abundant on the tip of the nose and 

 the balls of the feet. The sebaceous glands are very numerous 

 all over the body. Both are of microscopic size. 



A still more important part of the excretory system is the 

 urinary system, consisting of the kidneys, two ureters leading 

 from the kidneys to the bladder, the bladder, and the urethra. 



The student should note that the kidney is not enveloped by 

 the peritoneum, like the other abdominal organs, but lies dorsad 

 to it and is encased by a fibrous covering known as the capsule. 

 The hilus is that portion of the concave surface where the renal 

 artery and vein and ureter enter. A median longitudinal sec- 

 tion of the kidney will show that the ureter within the kidney 

 enlarges, forming the pelvis, into which projects the renal 

 papilla (Fig. 98). This is better demonstrated in a transverse 

 section. 



The substance of the kidney is composed of an outer cortical 

 layer, about a half centimeter thick, and an inner medullary 

 substance adjacent to the pelvis, and projecting into the latter 



198 



