FORMATION OF STAPEDIAL PLATE 87 



He regards (p. 380) the columella of reptiles as a homologue 

 of the upper end of the hyoid arch, but derives the operculum 

 from the chondrocranium. On p. 386 he states: 



To the labyrinth region belongs still another bone which springs up 

 from the pterygoid to the parietal — the columella. It has a cartilaginous 

 Grundlage (Leydig) which is laid down on a process of the chondro- 

 cranium (Gaupp) and which is also distinguishable in amphibia and 

 evolves itself in lacertilia into a columnar form which is characteristic 

 of it. 



It is difficult to see by what line of reasoning this latter colu- 

 mella could be regarded as belonging to the labyrinth region. 

 It is much farther removed from the labyrinth region than a 

 great deal of the pterygoid itself from which it is derived. This 

 evident error would be of minor interest if it had no counterpart 

 in the writings of more recent observers. Schimkewitsch, 

 (Lehrb. d. vergl. Anat,, p. 121) describing the conditions in 

 Sphenodon, states: ''From each pterygoid there reaches up a 

 'platten formig' bone (anti-epipterygoideum or columella cranii) 

 which represents a process of the palatoquadrate which has 

 already existed before in anuran amphibians." Although he 

 deals with the homologies of this bone in almost all groups of 

 reptiles, he neglects its description in the skull of the snake 

 (figures from Boas) where (figs. 134 and 135) the term columella 

 cranii is applied to the ear-ossicle whose internal end fits into 

 the fenestra ovalis. If these two columellae are homologous it is 

 puzzling that both should exist in the same reptilian form. 



In higher mammals the auditory 'columella' seems to be rep- 

 resented by the staff-like portion of the stapes. There seems 

 at present to be little doubt that the latter arises as a chondri- 

 fication in the mesenchyme of the second visceral arch; our ob- 

 servations concerning this point are not, however, in complete 

 unison. Concerning the origin of the plate-like cartilage which 

 forms the distal (distal from the point of view of the visceral 

 skeleton) portion of the stapes homologue which closes the 

 fenestra ovalis there is very great diversity of opinion. Accord- 

 ing to one view, the entire stapes including the stapedial plate 

 arises as a chondrification in the second visceral arch. Among 



