550 B. F. Kiiigsbuiy and II. 1). Kted. 



and tlieir modifications. In this study the following possible gen- 

 eral aspects were kept in mind: (1) The primary (primitive) and 

 secondary character of the connections and relations of the struc- 

 tures occupying the fenestra vestibuli more generally designated as 

 constituting the Columella auris, (2) comparison with the forms 

 below (fishes) the amphibian group (the hyomandibular homology), 

 (3) homolog}^ with the reptilian Columella and mammalian Ossicula 

 auditus, (4) the comparison and homology in Urodela and Anura, 

 (5) the relationships of the different urodele families, (6) the func- 

 tion and functional importance of these structures in the tailed 

 amphibia, (7) the variation in the arrangement of the parts of the 

 apparatus and its significance. 



It is not necessary to repeat here the reasons that led us to believe 

 an extensive re-examination of the comparative morphology of the 

 structures fitting into the fenestra vestibuli in urodeles to be neces- 

 sary, as they were briefly set forth in the first paper and previously 

 by others (Gaupp, '98; Driiner, '03). In the examination of the 

 different forms, there have been kept in mind the following morpho- 

 logical relationships : 



1. Relation (eouiiection by fusion, articulation or ligament) of the Colu- 

 mella (stilus cohmiellfe) to 



(a) the OS. squamosum (paraquadratum, Gaupp), 

 (&) OS. quadratum or palatoquadratum, 



(c) hyoid (ceratohyale) ; 



2. Relation to the carotid artery (Arteria carotis interna) and jugular vein 

 (Vena petroso-lateraMs) ; 



3. Relation to the otic capsule (lips of the fenestra restilruli) ; 



4. Relation to facial nerve (ramus hyonnnnlihularis VII) ; 



5. The ligaments coming into relation with the parts involved, — 

 (fl) Lipamentiim sqnamoso-colnmeUare, 



(?>) Lifiamentnm hiio-suspensoriale. 

 (e) Ligamentum liyo-mandihntarc, 



(d) Ligamentum hyo-cohnneUare ; 



6. Musculus operctilaris. 



Since early in the investigation it became apparent that there 

 were two morphologically distinct elements appearing in the different 

 forms, comparable, at least, if not homologous (vide subseq.) as we 

 believe with the plectrum (columella) and operculum in the frog, it 



