LIASSIC PLESIOSAURS. 2 7 



between the temporal fossas, and a continuation of the same crest, whose sides slope 

 away from each other at a right angle, characterises the upper part of the frontal to 

 midway between the orbits. The postfrontal bar, or flattened tract, dividing the 

 orbital from the temporal fossae, is an inch in breadth. The narrow nasals are 

 divided by a medial suture, and, with the prefrontal and lacrymal, separate the 

 orbit from the nostril. 



The lower jaw has slipped from beneath the cranium, and, by the effect of 

 the gradual pressure, has been turned, with the flatter left side upward. The angle 

 projects beyond the articular surface 2 inches 3 lines, terminating obtusely, slightly 

 bent, with the concavity upward, and 1 inch in thickness. The great part of the 

 articular cavity of the right ramus is exposed, showing a transverse diameter of 1 inch 

 3 lines, and a fore-and-aft diameter of 10 lines: it is concave lengthwise, sinuous 

 across. In advance of the articulation the ramus shows a depth of 1-| inch, gradually 

 increasing to that of 2 inches 3 lines, and then contracting vertically toward the 

 dentary part ; the deepest portion, formed by the angular and sub-angular elements, is 

 situated about four inches in advance of the articular cavity, and there the thin outer 

 parietes of the ramus have been crushed in, yielding to the superincumbent pressure. 



The length of the dentigerous part of the jaw is 1 foot 2 inches ; externally the 

 dentary descends vertically from the sockets containing the teeth, but internally it 

 swells out into a strong, convex, longitudinal tract, strengthening the alveoli, until the 

 two dentaries meet at the symphysis. There is a longitudinal groove at the middle 

 of the inner surface, below which the bone again swells out and is continued into the 

 thick under surface of the dentary. The length of the symphysis is nearly 7 inches ; 

 and here the vertical extent increases, and terminates more sharply below. The 

 vertical extent of the dentary, behind the symphysis, is 1 inch, the deepest part of the 

 symphysis is 1^ inch ; the outer surface of the symphysis is coarsely and irregulai-ly 

 rugose ; its upper ])order is scooped out at the alveoli for the larger teeth ; on the left 

 side there are about twenty-two sockets for teeth of different sizes ; the smallest are 

 behind, and the hindmost shows a straight crown (Tab. IX, fig. 6), sloping forward, 

 from 4 to 5 lines long, with the usual longitudinal ridges of the enamel. The tooth 

 in advance is sliglitly bent ; the eighth in advance shows a crown, 9 lines in length ; 

 the fifteenth in advance (Tab. IX, fig. 4) shows a sudden increase of size, and greater 

 degree of backward curvature ; including this, eight teeth occupy the rest of the 

 alveolar surface, which is coextensive with the symphysis. Here the teeth are divided 

 by intervals of rather more than their own basal breadth ; the largest tooth (ib., 

 fig. 3), following the curvature, has a crown two inches in length. The longitudinal 

 enamel-ridges begin at from one to two lines above the base of that covering of the 

 crown, where it is smooth, and they terminate about the same distance from the apex ; 

 they are least developed at the outer, convex part of the upper half of the crown. 

 Two of these large, laniary teeth project from the anterior alveolus, the outer and 



