THE SESAMOID ARTICULAR 



THE GANOIDS AND LUNG-FISHES. 

 Acipenser transmontanus, A. mikadoi. 



In this genus I find only two bones : the very large dentary, forming 

 the greater part of the mandible, and a small splint of bone lying on the 

 inner surface of Meckel's cartilage. (In large specimens a mento- 

 meckelian bone is developed in the anterior part of Meckel's cartilage 

 and forms a third element.) From its position the small inner splint 

 might either represent the sesamoid articular or the splenial. The tendon, 

 however, of the adductor mandibulae (or at least the muscle that func- 

 tions as such) is attached to the upper edge of the cartilage between this 

 inner bone and the dentary, and though some outer fibers of the tendon 

 are attached to the edges of both bones, the main attachment would sug- 

 gest that no sesamoid articular were present and that the inner bone 

 represents the splenial. It is the bone called the coronoid by W. K. Parker 

 in his Structure and Development of the Skull in Sturgeons (Phil. Trans., 

 1882, p. 173, pi. 18). In my specimens it is much larger than is shown 

 in Dr. Parker's plate, and is everywhere isolated from the dentary by 

 cartilage. 



Lepisosteus platostomus, L. osseus. 



Among the eight elements that make up the mandible of Lepisosteus 

 (two of which are presplenials) I find none that I can homologize with 

 the sesamoid articular, unless it be an inner shelf of the splenial in the 

 coronoid region. This is not in the typical region for the sesamoid 

 articular, being remote from Meckel's cartilage, and the only ground for 

 considering the possibility of this homology is that a stout adductor ten- 

 don is attached to it. A tendinous band also gives muscle attachment to 

 the edge of the supra-angular. I have examined several specimens of 

 various sizes down to 3^2 inches in length, but find no indication of this 

 inner splenial process as a separate element. 



