. Comparative anatomy. Anatomy, Comparative. TEETH 187 The elasmobranchs, indeed, do have a certain succession of teeth, Init only one at a time as single teeth are lost. Lower vertebrates, reptiles conspicuously, have a somewhat indefinite number of sets, and are said therefore to be polyphyodont. Only the mammals have two definite sets, and are therefore diphyodont. But monotremes, sirenians, and toothed whales retain their milk teeth throughout life, have no second set, and are said to be monophyodont. In general, then, the course of evolution has been from a large and indefinite number of
. Comparative anatomy. Anatomy, Comparative. TEETH 187 The elasmobranchs, indeed, do have a certain succession of teeth, Init only one at a time as single teeth are lost. Lower vertebrates, reptiles conspicuously, have a somewhat indefinite number of sets, and are said therefore to be polyphyodont. Only the mammals have two definite sets, and are therefore diphyodont. But monotremes, sirenians, and toothed whales retain their milk teeth throughout life, have no second set, and are said to be monophyodont. In general, then, the course of evolution has been from a large and indefinite number of simple teeth all alike, not fixed firmly in place, and borne by any part of the mouth, to a reduced and definite number, set firmly in alveoli, confined to the jaws only, and differentiated into three. 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 Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : P. Blakiston's Son
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