. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. now ANIMALS EAT. 65 r AfW^ ^<!^ Wlialo. In tlie former, the plates consist of closely set vertical hollow tubes; in the latter, the baleen, or whale- bone, plates, triangular in shape, and fringed on the inner side, hang in rows from the gums of the upper jaw. In some Whales there are about 300 plates composing the outer row in each jaw.^' True teeth, consisting mainh' of a hard, calcareous sub- stance called dentine^ are found only in back-boned ani- mals. They are distinct from the skeleton, and di
. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. now ANIMALS EAT. 65 r AfW^ ^<!^ Wlialo. In tlie former, the plates consist of closely set vertical hollow tubes; in the latter, the baleen, or whale- bone, plates, triangular in shape, and fringed on the inner side, hang in rows from the gums of the upper jaw. In some Whales there are about 300 plates composing the outer row in each jaw.^' True teeth, consisting mainh' of a hard, calcareous sub- stance called dentine^ are found only in back-boned ani- mals. They are distinct from the skeleton, and differ from bone in containing more mineral matter, and in not showing, under the microscope, any minute cav- ities, called lacuncB. A typical tooth, as found in Man, consists of a central mass of dentine, cap- ped with enamel and surrounded with cement. The first tissue is always present, while the others may be absent. It is a mixture of animal and mineral matter dis- posed in the form of extremely iine tulles and cells, so minute as to prevent the admission of the red particles of blood. One modification of it is ivory, seen in the tusks of Eleithants. Enamel is the hardest tissue of the bod}', and contains not more than two per cent, of animal matter. It consists of six-sided fibres set side by side, at right angles to the surfaces of the dentine. Cement closely resembles bone, and is present only in the teeth of the higher animals. Teeth are usually confined to the jaws; but the number, size, form, structure, position, and mode of attachment vary Mith the food and habits of the animal. As a rule, ani- mals developing large numbers of teeth in the back part of the mouth are inferior to those having fewer teeth, and 5. Fig. 29.—Section of Human Mo- lar, enlai'oed: k, crown ; n, neck; /, fang; , enaniRl; d, dentine; c, cement; jj, pulp- Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colorat
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Keywords: ., bookcentury1800, bookdecade1880, bookpublishe, booksubjectzoology
