574 



Comparative Morphology of Chordates 



heavy armor investing the dorsal and lateral surfaces of the animal. 

 The occurrence of small bony plates in the skin of some cetaceans has 

 been asserted and denied. Otherwise, bony scales are not known to 

 occur in mammalian skin. 



HP 



1 



Pf%^S^|Sl ■JgRfig, 



SWEAT GLAND 



;'fFAT CELLS 



SWEAT GLAND^' 



Fig. 442. A section of the thickened skin of 

 the human sole. The stratum corneum is espe- 

 cially thickened on the sole and on the palm of 

 the hand. (Courtesy, Neal and Rand: '"Chor- 

 date Anatomy," Philadelphia, The Blakiston 

 Company.) 



In striking contrast to reptilian skin, the skin in most mammals is 

 richly glandular. The glands, however, are not the primitive mucous 

 glands. Mucus and hair would not combine to advantage. In mammals 

 the glands of the general integument are the tubular sweat-glands 

 (Fig. 446), secreting a more or less abundant watery fluid, and the 

 alveolar sebaceous glands, usually attached to the follicles of hairs 

 and secreting an oily substance (Fig. 443). These secretions protect 

 the skin from becoming unduly dry and keep it soft and pliable. In 



