THE SESAMOID ARTICULAR 



THE EVENTOGNATHOUS FISHES. 



Deltistes luxatus, here described, but Ictiobus bubalus, Chasmistes 

 brevirostris, Myxostoma aureolum differ only as noted. 



Meckel's cartilage appears as a short, deep, thin, somewhat quad- 

 rangular plate, situated rather high on the mandible. Posteriorly it 

 abruptly ends against the endosteal process of the articular. Anteriorly it 

 ends in a similar way against a portion of the dentary, which may repre- 

 sent the mento-meckelian ossicle of some of the Ganoids here incorporated 

 with the rest of the dentary. 



Fig. 7. CHASMISTES BREVIROSTRIS 



an, angular; d, dentary; epr, endosteal process; me, Meckel's cartilage; 

 sa, sesamoid articular. 



The sesamoid articular is a very large flat plate, somewhat triangular 

 in shape, its upper edge nearly even with the upper edge of the 

 mandible, and its lower about equally overlying Meckel's cartilage and 

 the endosteal process of the articular. It lies broadly, and is connected 

 rather firmly, against the articular, and its anterior end overlaps the den- 

 tary. This is unique to my knowledge, for in other forms it is confined 

 to the articular, though in the eels the dentary overlies it. In Chasmistes 

 the condition is the same, but in the other two forms the sesamoid articu- 

 lar does not reach to the dentary. Considerable variation was found in 

 this character (all specimens were of rather large size), and as it is of 

 secondary development it is of little importance. The tendon is large and 

 flat, and is attached to the middle of the upper edge of the sesamoid 

 articular. 



