General Features 



19 



Cells containing pigment (chromatophores : Fig. 263) may be present 

 in either the epidermis or dermis, but are usually more numerous and 

 more highly specialized in the dermis (Fig. 12). They may occur also 

 in the subcutaneous layer. Fat may 

 be more or less abundantly deposited 

 in the subcutaneous layer. Sensory 

 nervous structures occur in both 

 I he epidermis and the dermis. 



The vertebrate skin is prolific in 

 its production of specialized struc- 

 tures, some mechanically protective, 

 some glandular. The stratum cor- 

 neuni may be elaborated into horny 

 scales (Fig. 15), feathers, or hairs. 

 At the tips of the digits, it is shaped 

 into pointed claws, heavy blunt 

 hoofs, or flat nails (Fig. 13). It forms 

 the outer sheath of such "horns" as 

 those on the heads of cattle and sheep. 

 The plates of "whalebone" (baleen) 

 hanging from the upper jaw of tooth- 

 less whales (Fig. 584) consist of horny 

 integumentary substance. 



Either the epidermis or cells in the dermis may secrete a calcareous 

 substance which constitutes the several types of calcified scales of 

 fishes, including the bony scale, entirely dermal in origin, which char- 

 acterizes the great majority of fishes (Figs. 14, 15). In all vertebrates 



Fig. 12. Skin of lungfish, Proto- 

 plerus; section perpendicular to 

 surface; much enlarged, (c) Dermis 

 (corium); (e) epidermis; (</) multi- 

 cellular gland; (u) unicellular gland. 

 (Courtesy, Kingsley: "Compara- 

 tive Anatomy of Vertebrates," 

 Philadelphia, The Blakiston Com- 

 pany.) 



Fig. 13. Diagrams of (.4) nail, (B) claw, and (C) hoof, (e) Unmodified epidermis; 

 (u) unguis (outer plate); (s) subunguis (ventral plate). Upper figures, longitudinal 

 dorsoventral sections; bones of digit in solid black. Lower figures, terminal surface 

 of digit. The unguis and subunguis are thickened regions of the stratum corneum. 

 (After Boas. Courtesy, Kingsley: "Comparative Anatomy of Vertebrates," Phila- 

 delphia, The Blakiston Company.) 



