Mammalia: Skin, Muscles, Skeleton 



Orifice of duct 



Excretory duct 



577 



Excretory duct 



Subcutaneous fat 



Body of sudoriferous gland 



Fig. 446. Section of the human palmar skin showing an isolated sweat-gland. 

 (After Testut. Courtesy, SchaefTer: "Morris' Human Anatomy," Philadelphia, 

 The Blakiston Company.) 



In aquatic mammals, sweat-glands and sebaceous glands are more or 

 less reduced or entirely lacking. 



There are also various localized and specialized glands, such as 

 wax (ceruminous) glands in the external ear, tear (lacrimal) 

 glands, and various scent-glands, usually anal in location (e.g., in 

 the skunk). The mammary glands are highly specialized integu- 

 mentary glands situated in paired organs on the ventral surface of the 

 body, secreting milk for nourishment of the young after hatching or 

 birth. These milk-glands are the especially distinctive glands of 

 mammals. 



Mammary Organs. A mammary organ consists of one or more 

 milk-secreting glands whose ducts, except in monotremes, open 

 upon or into an externally protruding nipple or teat. A milk -gland 

 is usually of the alveolar type (said to be tubular in monotremes) and 

 always so elaborately branched that a single gland becomes a large 

 mass of secretory tissue. When several such glands are present in one 

 mammary organ, they form a bulky mass lodged in the dermal and 

 subcutaneous layers and causing an external elevation of the skin. But 



