Lower Jaws
A study of the well preserved jaws of No. 1411, not only shows the exact number of elements composing the mandible as six pairs of bones; but it also indicates clearly the extent and relative positions of these elements, particularly those bones
Fig. 1. Internal view of the right mandibular ramus of Baptanadon natans (No. 1441). One fourth natural size. art., articular.; ag., angular ; cor., coronoid ; for., foramen ; s.ag., surangular , spl. splenial ; sym., beginning of the symphysis.
composing the posterior portion of the rami, which previous to the discovery of this specimen had not been well understood.
This specimen (No. 1441) gives the first positive knowledge of the shape and extent of the coronoid in Baptanodon. Figs. 1 and 2 show it to be a thin plate of bone extending along the inner side of the posterior end of the ramus. Its lower 
Fig. 2 Cross-section of posterior end of left mandibular ramus of Baptanodon natans (No. 1441). Natural size. art., articular ; ag., angular ; cor., coronoid ; s.ag., surangular. border laps along the upper internal border of the angu-lar except anteriorly where it overlaps the posterior prolongation of the splenial. The anterior termination is somewhat in advance of the node-like protuberance developed upon the upper border of the surangular, where it is overlapped by the posterior end of the splenial. Posteriorly the coronoid is narrow, and laps along the articular, thus assisting the surangular in holding that element in position. More anteriorly the coronoid widens rapidly, the upper margin being elevated in a dorsal process which is nearly the height of the protuber-ance on the surangular. Anterior to this process it grad-ually narrows to the point where it meets the overlap-ping splenial. The posterior end of the splenial, is wholly confined to the internal side of the ramus. The exact extent of the lower posterior prolongation could not be determined from this specimen. The splenials enter the symphysis and entirely separate the dentaries posteriorly.
