| OCR Text |
Show 492 DR. B. BROOM ON THE STRUCTURE [Apr. 19, throw a considerable amount of additional light on the structure of the jaw. One of the specimens includes a large part of both mandibles and shows two sections of the jaws-one through the angle and the other considerably further forward. These are shown in figs. 9 & 10, Plate X X X V . In fig. 9 the section is through the anterior part of the coronoid process. On the inner side of the large dentary near the middle is seen the small surangular, with below it two other bones which I believe to be the articular and the angular respectively. In the more anterior section (fig. 10) the surangular has almost disappeared, and below it there are three bones seen on section. The upper two are probably both articular- the inner of the two almost certainly, while the lowermost element is the angular. The detached portion of the dentary at the bottom is due to a very short process at the angle. The other specimen is the almost perfect articular region of the jaw. It is represented in PI. X X X V . figs. 4, 5, & 6. The broad articular is seen to be also fairly deep, and on passing backwards it is seen to divide into an upper and a lower process. It is supported on the outer side by the angular. Above the articular is the dentary. Though in the specimen there is a slight gap between the bones, it is probable that the dentary rested on the articular. It will be seen that the dentaiy has a posterior process which comes very near to the articulation. With regard to the mandible of Gomphognathus kannemayeri, 1 am unable to accept as conclusive the first two of the text-figures that accompany Seeley's paper (3). I am of the opinion that in the first figure the drawing does not distinguish between the delicate coronoid itself and plaster that has been added to the specimen. In figure 2 the drawing does not adequately represent the back part of the actual specimen, on account of the omission of the angular bone. The specimen is especially valuable in that the jaws are open wide, and a view is thus obtained of the anterior surface of the quadrates. Fig. 2, Plate X X X V . , represents the appearance of the articular region, the posterior part of the jaw being seen from above and the articular region of the skull from the front. Fig. 3 is the corresponding region of the opposite side. (When the specimen was first described by Seeley, the back part of the left jaw was broken off and apparently believed to be lost. Fortunately this portion is still preserved, and is now united with the rest of the specimen.) In the lower jaw is seen the back part of the dentary, consisting of the flat part which rests on the articular and the thin coronoid process (cf fig. 6). Beyond the dentary and to the outer side is seen the articular end of the articular bone. The whole structure of the articular region of the jaw is very similar to that in Cynognathus. The articular is, however, developed more ^ outwards, and the angular, which passes slightly further back on it, is mther more strongly developed. On both the right side and the left the quadrate bone appears |
