208 
PROF. D. M. S. WATSON AND MR. E. L. GILL ON THE 
lower upward into the oral surface ; this surface is covered with the shiny 
punctate surface now recognized as characteristic of a cosmoid bone. This 
region projects forward, and is sharply marked off from the rest of the lower 
jaw by depressions on the nearly vertical lateral surfaces. 
The dentary articulates with three other bones which lie on the outer 
surface of the jaw ; these are, a very small splenial lying anteriorly on the 
flat under surface of the chin, a somewhat larger post-spleuial which forms 
part of the floor of the lateral depression, in addition to a large part of 
the ventral surface, and a very large angular which extends backward to 
articulate with the articular. 
Fig. 34. 
Diptenis platyceplmlus (Ag-.). Dorsal and Yentral views of the lower jaw, with iiiuer and 
outer aspects of the left ramus, x IJ. Restored from iSIo. L. 10858, Manchester Museum. 
Ang., angular; Art., articular; Den., dentary; Po.Sp., post-splenial = preaugular ; 
Pn.AnT., pre-avticular ; Sp., splenial. 
The presence of splenial, post-splenial, and angular elements is clearly 
confirmed by No. 1878.5.166, Royal Scottish Museum, where these bones 
are seen from the dorsal aspect, the tooth-bearing bones being removed. 
The articular is a vei-y large bone, with a well-defined condylar surface 
formed by a deep cylindrical excavation running across its hinder surface 
