. An introduction to the study of mammals living and extinct. Mammals. Fig. 157.—a, Grinding surface of unworn molar tooth of AncMihirmm; &, corresponding surface of unworn molar of young Horse ; c, the same tooth after it has- been some time in use. The uncoloured portions are the dentine or ivory, the shaded parts the cement filling the cavities and surrounding the exterior. The black line separating these two structures is the enamel or hardest constituent of the tooth. in the early forms were very short (see Fig. 158, a); there was a distinct constriction, or neck, between the crown an
. An introduction to the study of mammals living and extinct. Mammals. Fig. 157.—a, Grinding surface of unworn molar tooth of AncMihirmm; &, corresponding surface of unworn molar of young Horse ; c, the same tooth after it has- been some time in use. The uncoloured portions are the dentine or ivory, the shaded parts the cement filling the cavities and surrounding the exterior. The black line separating these two structures is the enamel or hardest constituent of the tooth. in the early forms were very short (see Fig. 158, a); there was a distinct constriction, or neck, between the crown and roots; and when the tooth was developing, as soon as the neck once rose fairly above the alveolar margin, the tooth remained permanently in this position. The term " brachydont " expresses this condition of teeth, the mode of growth of which may be illustrated by those of man. The free surface had two nearly transverse curved ridges, with valleys between (Fig. 157, a); but the valleys were shallow and had no deposit of cement filling them, the whole exposed surface of the unworn tooth being formed of enamel. When the ridges became worn down the dentine of the interior was exposed, forming islands surrounded by enamel. With the progress of time the crowns of the teeth gradually became longer, the valleys deeper, and the ridges not only more elevated but more curved and com- plex in arrangement. To give support to these high ridges and save them from breaking in use, the valleys or cavities between them became filled up to the top with cement, and as the crown wore down an admirable grinding surface consisting of patches and. 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 Flower, William Henry, 1831-1899; Lydekker, Richard, 1849-1915. London, A. and C. Black
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Keywords: ., bookauthorly, bookcentury1800, bookdecade1890, booksubjectmammals
