674 COMPARATIVE ANATOMY 



glands, which are vitally secretory and tubular, and the acinous glands, 

 many of which are lobed and necrobiotic, although both originally arise 

 in connection with the hair. 



The secretion from the sweat glands is usually thin and watery, 

 although it may vary from this to a thick viscous pinkish fluid, the so- 

 called "blood-sweat" of the hippopotamus. 



The sweat glands may be found almost anywhere on the entire body 

 or they may be localized. Localization takes place most frequently in 

 the paws or on the palms of the hand and soles of the foot. Here they 

 serve to assist in grasping a given object more solidly. 



A modification of these glands also furnishes the oily secretion of 

 the ear. 



It probably has been observed that in hot weather horses sweat 

 quite pirofusely while dogs do not. This is due to the fact that horses 

 have sweat glands in the skin while dogs have not, so that dogs can only 

 obtain the same relief that other mammals obtain, during such weather, 

 by opening their mouths and panting, as it is only in this way that the 

 constantly accumulating moisture finds its way to a surface where evap- 

 oration then brings about a cooling. Muzzles should, therefore, always 

 permit the o x pening of the mouth. 



There are some races of men, such as the Fuegians, who likewise 

 have few sweat glands. 



The acinous glands furnish an oily secretion, apparently for the orig- 

 inal purpose of lubricating the hair, regardless of how far removed from 

 this function such glands may ultimately come to be. These glands are 

 called sebaceous. The tarsal or meibomian glands of the eyelids are 

 practically hypertrophied sebaceous glands of the eyelashes. These 

 meibomian glands pour out an oily secretion which lubricates the edge 

 of the lids and prevents tears from overflowing. There are modified 

 sebaceous glands in the various orifices^ of the body such as in the lips 

 and about the anus. 



Then there are groups of glands which are localized for quite specific 

 functions, such as the anal-sacs of the skunk which secrete a protective 

 substance, and the sexually attractive glands such as that of musk or 

 civet. Musk is often used in the manufacture of perfumes. 



Glands usually open as an elevation at a single place known as a 

 glandular area. The milk-glands of mammals are typical examples, but 

 there are cases where there is a sinking of the area so that instead of 

 the young taking a nipple in their mouths, the lips of the sunken area 

 fit Closely about the nose of the young and thus prevent the secretion 

 from being lost. Such is the case in Echidna (Figs. 383, 399). In the 

 opossum the nipple is really a sac like that in Echidna but turned inside 

 out. 



;, -! It is a common observation that in many of the domesticated ani- 

 mals there is a row of nipples extending from axilla to the groin. In the 



