. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. THE SKIN AND SKELETON. 135 "; The latter is an outer layer of minute ovei-- lapping scales, which are directed toward the point, so that rubbing a human hair or fibre of wool be- tween the thumb and finger pushes the root-end away. The root is bulbous, and is contained in a mi- nute depression, or sac, formed by an infolding of the skin. Hairs are usually set obliquely into the skin. Porcupine's quills and Hedgehog's spines make an easy transition to feathers, which differ from hairs onl
. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. THE SKIN AND SKELETON. 135 "; The latter is an outer layer of minute ovei-- lapping scales, which are directed toward the point, so that rubbing a human hair or fibre of wool be- tween the thumb and finger pushes the root-end away. The root is bulbous, and is contained in a mi- nute depression, or sac, formed by an infolding of the skin. Hairs are usually set obliquely into the skin. Porcupine's quills and Hedgehog's spines make an easy transition to feathers, which differ from hairs only in splitting up into numerous laminae. They are the most com- plicated of all the modifications of the epidermis. They consist of a "quill" (answering to the bulb of a hair), and a "shaft," supporting the " vane," which is made up of " barbs," " barbules," and interlock- ing "; The quill alone is hollow, and has an orifice at each end. The teeth of Mollusks and Articulates are also epidermal structures; but the teeth of Verte- brates are developed from the der- mis. In all cases, teeth belong to the exoskeleton. A human tooth and an oyster-shell rep- resent each other, structure for structure, (2) The Endoskeleton, as we have seen, has its first rep- resentative in the Cuttle-fish. AVith this exception, it is peculiar to Vertebrates. In the Cuttle-fish, and some Fishes, as the Sturgeon and Shark, it consists of carti- lage; but in all others (when adult) it is bone or osseous. Fig. ins.—Parts of a Feather: a, quill, or barrel; b, shaft; c, vane, or beard ; d, accessory plume, or down ; e, /, lower and upper umbilicusi, or ori- fire, leading to the interior of the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Orton, James, 183
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Keywords: ., bookcentury1800, bookdecade1880, bookpublishe, booksubjectzoology
