GILMORE : NOTES ON OSTEOLOGY OF BAPTANODON ON 
LowER JAws. 
A study of the well preserved jaws of No. 1441, 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 
Fie. 1. Internal view of the right mandibular ramus of Baptanodon 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 
border laps along the upper internal border of the angu- 
lar except anteriorly where it overlaps the posterior pro- 
longation 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 thesurangular. 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 
Fie. 2. Cross-section of posterior 
end of left mandibular ramus of Bap- 
tanodon natans (No. 1441). Natural 
size. art., articular ; ag., angular ; 
cor., coronoid ; s.ag., surangular, 
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. : 
