SUMMARY 



Specimens from nearly every important group of fishes have been 

 examined and are herein reported upon. The sesamoid articular was 

 found in every group that is more highly specialized than the primitive 

 Clupeoid fishes as well as in one of the Ganoids, Amiatus, though here its 

 identity may be open to some doubt. 



The sesamoid articular is variable in size and somewhat in position, 

 though it is always in relationship with Meckel's cartilage usually in 

 very close association with it. Typically, as in the perch-like fishes, it 

 is rather small and more or less covered by Meckel's cartilage. Some- 

 times, as in Albula, it is as large as the endosteal process ; or, as in some 

 of the Synentognathous fishes, it is so large that it projects above its sur- 

 rounding elements, so that it is visible from the outer surface. Sometimes 

 it is loosely attached to the mandible and is easily pulled away with its 

 tendon. Sometimes it is attached to the mandible by a dentate suture and 

 is disarticulated with difficulty. Usually it is more or less broadly at- 

 tached to the ectosteal plate of the articular, but sometimes only narrowly 

 attached, and occasionally scarcely, or not at all, in contact. Sometimes 

 it lies saddle-like over the top of Meckel's cartilage, remote from any bone. 

 It is variable in its connection with the endosteal process, but as the at- 

 tachment may depend upon the extent of the ossification of Meckel's 

 cartilage to form the process, this is without significance. In at least 

 one case (Lew gnathus) two equally stout, dense tendons join the sesa- 

 moid articular at a considerable distance from each other. 



The sesamoid articular is doubtless, as its name implies, a sesamoid 

 bone. This is especially well shown in Spheroides annulatus, where the 

 adductor tendon has obviously ossified for a short space, leaving an 

 interval of tendon between the ossified portion and the mandible. Inter- 

 mediate between this condition and the more typical condition is the sesa- 

 moid articular of Ovoides, a close relative of Spheroides, where the inter- 

 val of cartilage between the tendon bone and the mandible has disappeared 

 and the former has spread out to some degree on the mandible. 



On the other hand Microgadus and Gadus appear to have the bone 

 partly endosteal in origin, or at least a bone endosteal in origin has be- 

 come anchylosed with it. In Gadus, however, it is not altogether clear 



