Class 6. Mammalia. 



469 



one (Ruminants) . The glands or mammae, which vary in number (one 

 to seven, most in those animals which produce many young ones at a 

 time), lie in two rows on the ventral aspect of the body. They ai'e 

 of considerable size and much branched ; the terminations are 

 vesicular, and for this reason the glands were formerly regarded as 

 sebaceous ; comparison with those of Monotremes demonstrates, how- 

 ever, that they are really sudoriparous. During gestation the mammary 

 glands increase in size and complexity, auJ are functional for some 

 time after parturition. Milk is a watery liquid in which are suspended 

 numerous oil globules; these impart its white appearance. At the 

 close of lactation the glands become simpler again ; they are usually 

 rudimentary in the males. 



Specially modified skin glands, isolated or in patctes occur more rarely, but 

 still fairly frequently. As a rule the skin is invaginated to form a pit, covered 

 with hairs, and in this region the glands are specially prominent : such are the 

 interdigital glands of Sheep and other Ruminants ; the so-called lachrymal pits 

 in front of the eyes of the Red Deer; the perinseal pouches opening, in the Dog 

 and other Oarnivora, at the sides of the anus ; the musk sac in the Musk deer, etc. 

 In other cases the highly-developed skin glands open fi-eely on to the surface ; a 

 very large one opens on the back of the Peccary ; in certain Shrews there is a 

 region of the skin with numerous specially modified glands, etc. 



On the lower side of the foot there is usually a naked elastic tract 

 of skin, the sole, covered by a thick but soft stratum corneum, and 

 provided with numerous sweat glands. In some cases it extends over 

 the whole ventral surface, or it is limited to certain regions, namely, 

 to the toes. 



Like Reptiles and Birds, Mammals have cap-shaped claws at the 

 tips of the digits, and here also they are differentiated into two parts. 



Fig. 380. .4 Claw 

 of a Mammal (removed 

 from the subjacent skin) , 

 B Nail of a monkey, C 

 hoof; diagrammatic, s 

 sole (of the olaw) ; the 

 lest, wall. 



a harder dorsal (and lateral) wall, and a ventral horny sole, 

 consisting of looser horn; the base of the claw is oblique, so that 

 the sole is shorter than the wall; the latter forms a horny plate, 

 arphed longitudinally and transversely, whilst the former is flattened 



