288 



P. H. EDGEWOETH. 



liaupt. . . ." The development, however, in Ceratodus, of 

 a coraco-mandibularis, of coraco-branchiales, of a byoman- 

 dibula, and of a dorso-ventral sheet Cgvd behind the hyoid 

 bar, are all secondary to more primitive conditions present in 

 Amphibia. 



Goodrich was of opinion that ''the Dipnoi are probably a 

 specialised offshoot from the Teleostoman stem which 



Text-fiCt. 88. 



Rabbit, emljryo 7 mm., longitvidinal vertical section. 



acquired an autostylic structure before the hyomandibula 

 had become very large and before the hyostylism had become 

 fully established." The non-division of the mandibular 

 myotome and the persistence of the doiso-ventral sheet 

 Covd are, however, more primitive features than exist in 

 Teleostomi; and in the embryo of Ceratodus there is 

 a hyomandibula, the relations of which are different from 

 those occurrin"- in Teleostomi. 



