. Journal of morphology . ducibranch skulls just described, e. g. WotopJi-tJialmus (PI. XVII) and Cj/nops (PI. XVIII), the vestibule is in the form ofa smooth bulla, with the stapes set on behind; and that plate is either quitesoft or very slightly ossified; it is also relatively small. In Spelerpes (PI. XXI, Figs. 2, 3, and PI. XVIII, Fig. 10) the vestibuleis but little protuberant; its fenestra is lateral, and corresponding with thestapes, very large. The Columella Auris in Amphibia. 579 Despite the depression for the M. opercularis the ear capsule hasin this region a bulging appearance due
. Journal of morphology . ducibranch skulls just described, e. g. WotopJi-tJialmus (PI. XVII) and Cj/nops (PI. XVIII), the vestibule is in the form ofa smooth bulla, with the stapes set on behind; and that plate is either quitesoft or very slightly ossified; it is also relatively small. In Spelerpes (PI. XXI, Figs. 2, 3, and PI. XVIII, Fig. 10) the vestibuleis but little protuberant; its fenestra is lateral, and corresponding with thestapes, very large. The Columella Auris in Amphibia. 579 Despite the depression for the M. opercularis the ear capsule hasin this region a bulging appearance due to the growth of the fenes-tral plate backwards beyond the margin of the fenestra 47 (PI. VI) shows not only that the prominence has extendedbeyond the margin of the fenestra, but also that within the promi-nence there is a recessus which is continuous with the cavum peri-lymphaticum. Earlier in this paper it has been shown that in Ambystoma andothers there is a perilymphatic prominence in the region of the. TAii^^—-^ Figs. G and 7. Plethodou cinereus, embryo. C, arteria carotis iuterna;, canalis lateralis; Col., columella; H., ceratohyale; , ligamentumhyo-columellare; M., musculus cephalo-dorso-mandlbularis. Sp., os squa-mosum ; , vena petroso-lateralls. fenestra vestibuli formed by the outward and backward growth ofthe operculum and that to the lateral aspect of this structure the is attached. Within the perilymphatic prominence isthe recessus perilymphaticus, a caudal continuation of the peri-lymphatic cavity. In these respects there is a striking similaritybetween the caudal portion of the fenestral plate in the Plethodon-tidse and the operculum of other forms. Further than the similari-ties mentioned in the preceding paragraph there is, in the adult, noevidence as to the constitution of the fenestral plate in the Pletho-dontidss. In the light of development, however, the condition is 580 B. F. Kingsbuiy and H. D. Keed.
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