No. 2.] HYOIDS AND OTICS OF BATRACHTA. 305 
follows that the osszcula auditus of the Batrachia Salientia must 
be excluded from the discussion of the homologies of the Mam- 
malian ossicula. 
Sixth. But the characters of the Ganocephala and Rhachi- 
tomi permit the following reflections, since the latter order is 
the one from which the Salientia derive their descent. The 
existence of a well-developed columella auris, which is unseg- 
mented, in the former orders, apparently like that of the Lacer- 
tilia, suggests that the segmentation seen in the Salentia is a 
specialization of later origin. This columella has also the posi- 
tion of the proximal part of the ceratohyal in the adult frog and 
the larval salamander. As the position of this element in all 
but the youngest tadpoles is a result of coenogeny, it may be 
inferred that the osszcula auditus of both the Rhachitomi and 
the Salientia represent the separated proximal end of that arch, 
and hence be truly homologous with the incus of the Mam- 
mal. The probability that this is the case is increased by the 
character of this element in the Pelycosaurian genus Clepsy- 
drops,! — where the columella extends to the cranial wall, leav- 
ing the stapes to one side. This is exactly comparable to the 
relation between the interstapedial and the stapes seen in the 
Salientia, except that the two elements are not actually con- 
nected, as in Clepsydrops. Palaeontology then modifies the evi- 
dence from embryology, and renders it probable that the 
columella auris of the Permian genera, the interstapedial, and 
the incus are homologous elements, and originated by segmen- 
tation from the proximal end of a ventral cranial arch, probably 
the ceratohyal. 
Seventh. It follows from what has preceded, that the con- 
dition of the representatives of the osstcula auditus in the 
Urodela is one of degeneration. 
Liighth. It becomes probable, but not certain, from the posi- 
tion of the tympanic disk in the Rhachitomi, at the proximal base 
of the quadrate bone, that the epistapedial cartilage has originated 
as a segmentation from the proximal extremity of the quadrate 
cartilage, and is therefore truly homologous with the Mammalian 
malleus. This is, however, nothing more thana probability. For 
a considerable part of the material described in the preceding 
pages I am indebted to the United States National Museum. 
1 See Proceedings American Philosophical Society, 1884, p. 41, Pl. I., Fig. 2. 
