CLASS MAMMALIA 



677 



Claws, Nails, Hoofs, etc. - -The claws of the UNGUICULATA, 

 the nails of the PRIMATES, and the hoofs of the UNGULATA are 

 all modifications of the horny covering' on the dorsal surface of 

 the distal ends of the digits. The chief forms are shown in 

 Figure 545. When on the ground the foot rests partially or 

 entirely upon the pads or tori (b). Dermal papillae occur on the 



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FIG. 545. Diagrammatic longitudinal sections through the distal ends 

 of the digits of mammals. A, spiny anteater, Echidna. B, an unguiculate. 

 C, man. D, horse. 1-3, phalanges; b. torus; X, nail-plate; 5, sole-horn; 

 IT, bed of claw or nail. (From Wiedersheim, after Gegenbaur and Boas.) 



tori, often forming concentric lines such as those that produce 

 the finger-prints of man. The sole-horn (S) is softer than the 

 nail-plate (X). 



Other epidermal horny thickenings are the horn-sheaths of the 

 ox and other ruminants, the nasal horns of the rhinoceros, and 

 the " whalebone " (baleen, Fig. 543) of certain whales. Dermal 

 plates of bone form the exoskeleton of the armadillos (Fig. 526). 



Cutaneous Glands. - Mammals possess a greater number of 

 glands than reptiles or birds; these are for the most part seba- 

 ceous and sweat-glands, or modifications of them. The sebaceous 

 glands usually open into the hair-follicles (p. 403, Fig. 347, Z>), 



