. Comparative anatomy. Anatomy, Comparative. Fig. 141.—Comparison in development and structure between a placoid scale and a tooth, a, b, and c represent the scale; d, e, and / the tooth. In all the figures the stratum corneum is dotted, the stratum germinativum is represented by a layer of large cells with nuclei; and the cutis is presented as composed of fibers with scattered cells. X, enamel membrane; y, cutis papilla; e, enamel; d, dentine; p, pulp cavity. (From Wilder's "History of the Human Body," Henry Holt & Co.) is secondarily replaced by ectoderm. Until such evidence is
. Comparative anatomy. Anatomy, Comparative. Fig. 141.—Comparison in development and structure between a placoid scale and a tooth, a, b, and c represent the scale; d, e, and / the tooth. In all the figures the stratum corneum is dotted, the stratum germinativum is represented by a layer of large cells with nuclei; and the cutis is presented as composed of fibers with scattered cells. X, enamel membrane; y, cutis papilla; e, enamel; d, dentine; p, pulp cavity. (From Wilder's "History of the Human Body," Henry Holt & Co.) is secondarily replaced by ectoderm. Until such evidence is presented, we have no alternative to the conclusion that the endodermal hning persists and produces both taste-buds and enamel. Whatever the origin of the enamel of these pharyngeal scales, there is no doubt that the enamel of the teeth, like that of dermal scales, is of ectodermal origin. Originally, in vertebrates, the teeth were for seizing and holding prey. Grinding and cutting teeth, tusks, and fangs, are all modifications of the primitive mouth trap. The number of these holding teeth is indefinite in elasmobranchs, which may have as many as one hundred. They are not attached to the jaws, but merely imbedded in the skin of the mouth. They are all about alike; and when one is lost, another moves forward into its 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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