616 B. F. Kingsbury and li. D. Reed. 



One of the characteristics of the urodele stilus is its early con- 

 nection with the ventral edge of the squamosum, and from the first 

 it has appealed to us as of profound morphological significance. 

 Its final interpretation, however, is not yet possible, and must await 

 the establishment of many facts of relation and development in the 

 domain of comparative morphology. Although from the develop- 

 ment of this bone over the lateral semicircular canal in urodeles 

 (Kingsbury '03 ; Thyng '06) it is regarded by us as a squamosum, 

 other considerations led Gaupp to bestow upon it the indifferent 

 name of Paraquadratwn. Granting that it is a squamosum, its de- 

 velopment requires further study, and its value in urodeles, — as 

 Dermo-, Auto- or Amphisquamosum has to be considered. As an 

 Autosquamosum deriving its cells (primarily?) from the periotic 

 blastema, it may be pointed out that it has precisely the position and 

 relation to the proton of the columella that would be required of it 

 if the hyomandibular homology of the latter is accepted, since in 

 fishes it seems to afford a portion of the articular surface for that 

 bone. Nor do two considerations that immediately occur appear 

 necessarily antagonistic to this view; the first, that in the event of 

 the acceptance of the elasmobranch origin of the Amphibia, no squa- 

 mosum (as such) existed in the ancestral forms; the second, that 

 the larval connection of the columella with the squamosum is but a 

 step in the shifting of the suspensorium (palatoquadrate) during 

 growth, which in its second phase again transfers the connection to 

 the palatoquadratum or the os quadratum. 



The absence of any connection between the columella and the cera- 

 tohyal has possibly been most commonly regarded as the greatest 

 defect in the ontogenetic evidence for the hyomandibular homology. 

 Recognition of the existence of a columellar proton outside the otic cap- 

 sule, its relations to palatoquadrate, otic capsule, and facial nerve, 

 in comparison with the requirement of a first segment of the hyoid 

 arch, renders less important evidence of a connection of ceratohyal 

 and columella. Yet the evidence of an embryological relation of 

 the two structures seems stronger than is usually recognized. Miss 

 Piatt ('9.7), when describing the extra-otic origin of the columella 

 (her operculum) considered that its lack of connection vsdth the 



