42 PROCEEDINGS OF THE NATIONAL MUSEUM. ^ol. 57. 



the faintest doubt or uncertainty, it seems to me, in liomologizing 

 the succeeding element of the frog with that of the incus of the mammal. 

 The outstanding and all-important foundation for such a homology, 

 rests upon the fact that it articulates not only with the stapes by a 

 distinct facet, but it likewise articulates with the prootic, in the side 

 wall of the otic capsule, just as the short process of the incus is, 

 without exception, received into the fossa incudis in all mammals 

 and that, moreover, in the same identical position as in the frog. 

 This is not the case in any known reptile or bird living or extinct. 



If, therefore, we are thus enabled to establish the identity or 

 homology of these two important elements in the auditory chain of 

 Rana and the mammal, what of the remaining elements? They 

 must clearly then correspond to, and be homologous with the mal- 

 leus, the cartilaginous transverse portion, the ventral end of which 

 is fixed between the layers of the ear drum, representing the manu- 

 hrium, of tJie malleus, the dorsal end having probably degenerated 

 into the superior mallear ligament; and the osseous portion repre- 

 senting the head and tody of the lone in the mammalian auditory appa- 

 ratus. The correctness of this determination is further established 

 by the researches of Kingsley, who has conclusively shown that the 

 manubrium of the malleus arises as a separate element in the audi- 

 tory chain of the mammal.'^ 



That the mammalian auditory chain originally arose and was 

 developed from a chain of elements similar in all respects to that now 

 found in the Anourous Batrachia, there can be therefore apparently 

 little or no question whatever. If on the other hand the auditory 

 chain of the Eeptilia has always been characterized by the essential 

 features now displayed by the modern Sauropsida, then in that 

 ^vent they can not have had anything to do with the ancestry of the 

 Mammalia, however much they may have approached them in other 

 j-espects. These features are seen in the long styliform condition of 

 the stapes, the absence of any element corresponding to the incus, 

 which has attachment to both stapes and the side wall of the audi- 

 tory capsule, and finally, the union of the proximal end of the hyoid 

 arch with the auditory chain, instead of the auditory capsule itself, 

 •entirely independent of any part of the former. These differences 

 are fundamental and profound, and they map out most clearly and 

 distinctly the trend of the two lines of descent.^ 



1 The Ossicula Auditus, Tufts College Studies, vol. 1, pp. 203-274, 1900. 



s Huxley further states in the same article that in Menohranchns among the Urodela, in which there is no 

 tj-m panic cavity nor tj-mpanicmembrane, the stapes is relatively large and conical in form, from the conical 

 end of which a strong ligament passes to the posterior face of the suspensorium. The hyoidean apparatus 

 is represented, upon each side by a cartilaginous rod, subdivided into a short hypo-hyal and a long cerato- 

 hyal. A strong ligament extends from the face of the latter, below its free summit, to the suspeusoriiun, 

 reaching this at the same place as the stapedial ligament, into which it is continued. This in connection 

 with the styliform stapes of A mphiuma which is articulated directly to the posterior part of the suspenso- 

 rium , together with the strong hyo-suspensorial ligament and the weak hyo-mandibular ligament, seems 

 to foreshadow the sauropsidan condition of these parts in the Urodela, quite in the same manner that the 

 ^auditory chain of the Anoura foreshadows that of the mammal. 



