OSTEOLOGY OF AMERICAN PERMIAN VERTEBRATES 419 



in the ichthyological literature there are prior names for these ele- 

 ments in the crossopterygian fishes. 



Although there has been an unnecessary duplication of studies 

 which might have been avoided, the results are fortunate in 

 their independent corroboration, placing at rest any doubts as 

 to the real structure of the stegocephalian mandible. Dr. Broom's 

 figures are inaccurate in detail, as will be seen by comparing them 

 with those herewith given. 



A detailed description of the elements is unnecessary; the illus- 

 trations will explain them better. In none of the many specimens 

 have the sutures between articular and surangular been dis- 

 tinguished. I have spent much time in making sections of the 

 articular end and in corroding with acid many specimens, but 

 wholly in vain. There are certain variations in different specimens 

 which it may be well to notice. The posterior inframeckeHan 

 foramen is sometimes situated farther in advance, and is almost 

 wholly bordered above and below by the postsplenial. The splenial 

 usually enters very distinctly into the mandibular symphysis; 

 in some specimens it takes only a sHght part. A structure like 

 that of Trimerorhachis I have observed in Eryops, Diplocaulus, and 

 other stegocephalians. I also find the postsplenial in Anaschisma, 

 but have not distinguished the anterior coronoids. 



SUMMARY 



The mandible of the primitive amphibians differs chiefly from 

 that of the early reptiles in the division of the coronoid into three 

 elements, or possibly four, and in the division of the splenial into 

 two. The surangular cannot be distinguished, if present. 



