Trituberculy : a review dedicated to the late Professor Cope / by Henry Fairfield Osborn.

  • Osborn, Henry Fairfield, 1857-1935.
Date:
[1897]
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Licence: Public Domain Mark

Credit: Trituberculy : a review dedicated to the late Professor Cope / by Henry Fairfield Osborn. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    1897.] in front of the paracone and protocone, as shown in the dia- gram (Fig. 6). Thus the inferior entostylid is developed near the entoconid, while the superior hypostyle develops near the hypocone. The first of the inferior styles to develop is the “metastyle,” a reduplication of the metacone, the well known “ a-a ” of Rutimeyer. In all ungulates in which the “mesostyle” is developed the external cusps remain of the same size. In the tapirs no “mesostyle” appears, yet these cusps are symmetrical; but in the rhinoceroses, which also lack the mesostyle, the first fact to note is the asymmetrical growth of these cusps; the meta- cone is elongated while the paracone is reduced and crowded up against the parastyle. This point was observed by Cope in seeking for a definition of the Rhinocerotidse in 1875. The rhinocerotine molar, whether of Hyrachyus, Amonodon or Acer- atherium, has the further distinction that it is the only type in which a complete ectoloph is formed, and second, as Cope has already observed, the asymmetry of the external cusps is em- phasized by the flattened metacone and conic paracone. Fig- ure 2 illustrates also the three projections from the ectoloph, protoloph and metaloph, namely, the “crista,” “antecrochet ” and “ crochet.” These, with the three “ fossettes ” formed by them, were noted and named by Cuvier, and, as shown by Falconer, Flower, Lydekker and others, are of great specific value.2 We have already seen that Cuvier’s term “ fossette ” may be substituted for the “ cement lakes ” in the horse’s molar. The terms formerly adopted, or proposed, by Lydekker3, after English usage, and those in German and French usage, have already been given in the Table 2 As pointed out by Lydekker, the writer mistakenly transposed these terms ‘‘crochet” and “antecrochet” in a former paper, Bull. Mus. Comp. Zool., 1890, p. 81. J“Siwalik Rhinocerotidse,” Pal. Indica. Fig. 13.—Tapir Molars. Primitive Systemodon, and modern Tapirus.