4O THE SESAMOID ARTICULAR 



that the sesamoid articular in replacing a section of Meckel's cartilage 

 is necessarily the ossified cartilage. The sesamoid articular may have 

 surrounded Meckel's cartilage, and developing from without inward may 

 thus have replaced it. The beginning of such a process is suggested by 

 Melanogrammus, and other forms, where the sesamoid articular arches 

 over the upper surface of Meckel's cartilage. Such, however, does not 

 account for the condition in Micro gadus (M. tomcod), where the carti- 

 lage is ossified in a rod in front of the sesamoid articular. 



The fact that ossification has taken place in Meckel's cartilage sug- 

 gests an apropos observation of Dr. Ridewood's (Proc. Zool. Soc. Lond., 

 1904, p. 56) in regard to bones that are both ectosteal and endosteal in 

 origin, whether the two sorts are anchylosed or distinct from each other. 

 "The endosteal ossification has been set up in sympathy with the ossi- 

 fication taking place in the dermal tissues. The process of ossification is 

 infectious, if one may employ such a term in this connection." 



It is significant that in every case the sesamoid articular is in close 

 relationship with Meckel's cartilage (or with the endosteal process, which 

 is ontologically the same). Even in cases where it has developed 

 upwards towards the coronoid region it still retains its connection with 

 the primitive cartilage. 



Moreover, in some cases, as Albula, it is strikingly like the endosteal 

 part of the articular, and appears (at least superficially) to bear the same 

 relationship with Meckel's cartilage the cartilage apparently issuing 

 from it as it does from the endosteal process. 



Other tendons than that to the sesamoid articular join the mandible 

 at various places, sometimes originating on the same muscle and same 

 place as does that to the sesamoid articular; but they are nearly always 

 less compactly organized, though often they are larger. There is never 

 a second sesamoid articular developed for these other tendons, though 

 they may appear to be more important in doing the greater share of the 

 work. 



The sesamoid articular is of no use in taxonomy of groups larger 

 than species, as it often differs within the genus. To pronounce upon 

 its value in differentiating species, or upon its individual variation, would 

 necessitate much more work within narrower limits than has been here 

 undertaken. 



