File:The American journal of science (1908) (18153649551).jpg

Title: The American journal of science
Identifier: americanjourna4251908newh (find matches)
Year: 1880 (1880s)
Authors:
Subjects: Science
Publisher: New Haven : J. D. & E. S. Dana
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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388 Ji. S. Lull—Cranial Musculature in Dinosaurs. which bore the lower beak. The teetli form an admirable chopping mechanism, shearing vertically past those of the upper jaw. The worn face of the entire tooth series, however, is not a perfect plane but is slightly twisted, being somewhat oblique at the posterior and becoming vertical at the anterior end of the row. The worn faces of the individual teeth exhibit in some instances tiny oblique stride passing upward and backward across the enamel in those of the lower jaw. These would seem to indicate the direction of wear. The articulation of the jaw is such as to permit some freedom of
Text Appearing After Image:
ptm. Fig. 1. Under side, rear, of lower jaw of Triceratops. motion, and, judging from these facts, it would seem as though the jaw movement was in the main vertical, with a slight lateral motion either to the right or left at the beginning of the upward movement. When the final closure is reached the jaws would, however, be in perfect alignment, enabling the upper and lower beaks to form a perfect, turtle-like shear. There may have been a slight movement to the rear, which would account for the oblique strise on the teeth; a forward movement would of course be out of the question on closure, as it would cause the wedge-shaped mechanism to bind. Muscle insertions are indicated on the jaw, first on the rear margin of the very high coronoid process for the temporal muscle; on the inner lower margin of the splenial and dentary for the pterygoid muscles and on the lower face of the articular, angular, and splenial for the digrastric or depressor mandibuli (fig. 1). A passage on either side leads upward and backward within the bones of the cheek, above the quad- rate and exoccipital, and finally opens upon the upper surface of the frill through the supratemporal fossa. These are evidently the tracts wherein lay the temporal muscles, having

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