1908-9.] Development of Auditory Ossicles in the Horse. 597 
Rabl, Gaupp, and many others. As we have seen, the malleus and incus 
are derivatives of the first arch ; their articulation satisfies the proper 
conditions ; they are so similarly related to the chorda tympani and to the 
seventh nerve that I feel it unnecessary to argue at great length that they 
are homologous with the articulare and quadrate. Moreover, Gaupp’s 
discussion of that question is admirable, and may be considered final. The 
hypothesis held by Gadow, Albrecht, in part by Fraser and some others, 
that either one of these two elements is a derivative of the second arch, 
will not bear close analysis. 
Parker, followed by Gaupp’s first position, and Fuchs, together with 
many other investigators, have believed the stapes to be derived from the 
auditory capsule either wholly or in part, thus making it homologous with 
the sauropsidan stapedial apparatus. Others, as Gadow, Albrecht, Wieder- 
sheim, and many more, have believed the stapes to be homologous with the 
hyomandibular of fishes. As to the conditions met with in the Amphibia, 
I know them only through the literature. Miss Platt gives for necturus 
the fact that the operculum arises independently of the auditory capsule, 
and Killian for axolotl, whilst Stohr for triton and siredon derives the 
operculum from the anterior boundary of the fenestra. For the Anura he 
derives the operculum from a different portion of the auditory capsule. 
Fuchs, however, has I think clearly shown that the amphibian stapes is 
derived from the auditory capsule and the extra-collumella from the hyoid 
arch. The conclusion is at once drawn that the mammalian stapes is on 
no account homologous with the sauropsidan operculum plus the accessory 
parts. Peter has shown in the development of the skull of Ichthyophis 
glutinosis that the stapes is closely connected to the quadrate. But the 
stapes-quadrate connection is in the vicinity of the quadrato-mandibular 
articulation, whilst the mammalian stapedo-quadrate connection is at an 
entirely different region. 
Unless it can be shown, then, that the Amphibia develop two types of 
accessory auditory apparatus, it is impossible to consider the mammalian 
stapes as a representation of any structure found in the Amphibia and 
reptiles. 
And inasmuch as the hyomandibula of fishes is a derivative of the 
second arch, it is impossible to conclude that the mammalian stapes 
is homologous with it ; and the stapes cannot be a portion of the 
quadrate, because it is chondrified from a separate centre. Moreover, 
there are no other possible homologues, and therefore one is forced 
to conclude that the mammalian stapes has no homologue in the lower 
Vertebrata. 
