614 B. F. Kingsbury and H. D. Eeed. 



in which it does come in contact with the periotic cartilage, no trace 

 of a thinning or fenestration results. Commenting on the position 

 of the hyomandibulare between palatoquadrate and the otic capsule, 

 he expressed the conviction that we must look for the ancestors 

 of terrestrial vertebrates in the low elasmobranchs (Notidanidse and 

 Pro-Selachia) in which the hyomandibulare has no part in the sus- 

 pension of the jaw, but affords the hyoid arch an independent articu- 

 lation with the skull. 



Since our results bear directly on the problem and from some points 

 of view, at least, seem to strengthen the homology of the amphibian 

 columella auris with the hyomandibulare, illuminating some of the 

 obscure points of development and relation, it seems desirable to 

 consider it briefly from the following view-points: (a) the extra- 

 otic origin of the columella, (b) the relation to the palatoquadrate, 

 (c) the connection with the squamosum, (d) the relation to the facial 

 nerve, (e) the relation of the columella auris to the ceratohyal. 



As Fiirbringer pointed out in the discussion of the paper of 

 Fuchs, Salamandra is highly specialized and not a form upon which 

 to base conclusions of general applicability. This has been mark- 

 edly illustrated in this very problem. For the present, the operculum 

 (our use) may be regarded as a part of the otic capsule both in this 

 and the other forms, that possess this structure. Fuchs, however, 

 dealt with but half the problem, as has been shown (p. 568). By 

 other workers, in other forms evidence has been given of an extra- 

 otic origin of a part, at least, of the fenestral structures: — In ISTec- 

 turus by Miss Piatt and by Kingsbury (not published) ; in Ambys- 

 toma by Killian and by ourselves in this paper ; in Cryptobranchus. 

 Spelerpes and Plethodon, in this paper. In these salamanders, and 

 doubtless in all forms possessing a well developed columella (our 

 use), the first appearance of the sound-transmitting apparatus is as 

 a group of cells outside the otic capsule. Of this the evidence seenis 

 quite strong ; it is only necessary to refer once more to the figures 

 illustrating the condition (PI. IV, Fig. 39 ; PI. VII, Figs. 52 and 

 53; Text Figs. 6 and Y). In the growth of this blastema in close 

 association with the otic capsule, the chondrification as stilus and 

 fenestral plate, there is introduced the difficulty mentioned by Gaupp, 



