. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. made up of large dermal plates (Fig. 36d), which were usually embossed in bas relief, and sometimes bore along the back formidable spines project- ing upward two feet or more. The corium in modern reptiles plays a secondary role, while the epi- dermis reaches perhaps a greater elaboration than in any other group of vertebrates. Among birds and mammals scaliness is of ex- ceptional occurrence. The scaly legs and feet of feathered birds (Fig. 149) reveal the
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. made up of large dermal plates (Fig. 36d), which were usually embossed in bas relief, and sometimes bore along the back formidable spines project- ing upward two feet or more. The corium in modern reptiles plays a secondary role, while the epi- dermis reaches perhaps a greater elaboration than in any other group of vertebrates. Among birds and mammals scaliness is of ex- ceptional occurrence. The scaly legs and feet of feathered birds (Fig. 149) reveal their reptilian an- cestry, while there are a few scale-specialists among mammals. 7. Birds Anyone who has ever attempted taxidermy i u i ti- i -i * • i • Fie. 149. Scaly foot of knows how loose, thin, and easilv torn is the skin & '. . J . an osprcy. (After of a bird. Those parts not covered by feathers, like Schaff.) the shanks and the bare areas around the base of the beak, exhibit a thickened corneal layer of epidermis, but everywhere else not only the epidermis but also the corium is reduced to a delicate thinness. The typical looseness of a bird's skin, so unlike the tightly fitting integument of the fishes, is an advantage in flight, enabling the muscles, unhampered by a binding integumentary covering, to contract freely and to change their shape easily. The looseness of the skin on the belly of penguins serves a special purpose adapted to icy an- tarctic conditions. During incubation the single egg is lifted off the frozen ground to a secure position on top of the webbed feet of the parent bird and a generous apron of loose skin from the region of the belly is snugly wrapped around the egg to keep it warm. Exoskeletal structures of birds, such as feathers, beaks, leg-scales and claws, are entirely epidermal, since dermal elements like the scales of fishes or the bony plates of certain reptiles are absent in this Fig. 150. Embryo of Erinaccus, the Europe
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