File:Image from page 448 of "On the anatomy of vertebrates (electronic resource)" (1866) (14753236974).jpg

Identifier: b20416039_001 Title: On the anatomy of vertebrates [electronic resource] Year: 1866 (1860s) Authors: Owen, Richard, 1804-1892 Subjects: Anatomy, Comparative Vertebrates Fishes Reptiles Mammals Birds Publisher: London : Longmans, Green Contributing Library: Wellcome Library Digitizing Sponsor: Wellcome Library

View Book Page: Book Viewer About This Book: Catalog Entry View All Images: All Images From Book

Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image: rnalstructure, by which this huge herbivorous extinct lizard deviatesfrom every other known reptile. As in the Iguana, the base of the tooth is elongated, contracted,and subcylindrical; the crown expanded, and smoothlyconvex on the inner side. When first formed, it isacuminate, compressed, its sloping sides serrate, andits external surface traversed by a median longitu-dinal ridge, and coated by a layer of enamel; but,beyond this point, the description of the tooth of theIguanodon indicates characters peculiar to that genus.Three longitudinal ridges, fig. 273, traverse the outersurface of the crown, one on each side of the medianprimitive ridge ; these are separated from each other, toothand from the serrated margins of the crown, by four of Igu^odon-wide and smooth longitudinal grooves. In the upper jaw theteeth are less curved, and are thicker transversely to the jaw:the primary ridge is much more prominent. The marginal ser-rations present, under a low magnifying power, the form of

Text Appearing After Image: 404 ANATOMY OF VERTEBRATES. transverse ridges, themselves notched, so as to resemble the mara-millated margins of the unworn plates of the elephants grinder.These ridges or dentations do not extend beyond the expandedpart of the crown: the longitudinal ridges are continued fartherdown, especially the median ones, which do not subside till thefang of the tooth begins to assume its subcylindrical form. At the earlier stages of abrasion, a sharp edge is maintained atthe external part of the tooth by means of the enamel whichcovers, and is restricted to, that surface of the crown. Theprominent ridges upon that surface give a sinuous contour to themiddle of the cutting edge, whilst its sides are jagged by thelateral serrations. The dentine next the enamel is harder thanthe vaso-dentine of the opposite half of the crown. When thecrown is worn away beyond the enamel, it presents a broad andnearly horizontal grinding surface, and another dental substanceis brought into use to give an inequali

Note About Images