. The Columella auris in Amphibia. 582 B. F. Kingsbmy and H. D. Keed. It appears that the definitive plate of the adult is the result of a direct and continuous growth of cartilage in the membrane which covers the foramen vestibuli. At no time during development are there found separate centers of chondrification in either stilus or fenestral plate. There appears to be a wide divergence between the sound-trans- mitting apparatus in the Plethodontidse and that in Ambystoma. This seems particularly true of the development, and as a consequence is also true of the homology of parts. A brief revie
. The Columella auris in Amphibia. 582 B. F. Kingsbmy and H. D. Keed. It appears that the definitive plate of the adult is the result of a direct and continuous growth of cartilage in the membrane which covers the foramen vestibuli. At no time during development are there found separate centers of chondrification in either stilus or fenestral plate. There appears to be a wide divergence between the sound-trans- mitting apparatus in the Plethodontidse and that in Ambystoma. This seems particularly true of the development, and as a consequence is also true of the homology of parts. A brief review of the devel- opment of the fenestral elements in the forms thus far considered may, therefore, render the situation easier to grasp. In Ambystoma the ear capsule chondrifies early and the columella fills the fenestra vestibuli. At transformation (there being no room for growth) the operculum is cut out from the cartilage of the ear capsule itself; an adaptation, it might seem, to mechanical needs. In Triton and Diemictylus the columella relatively early fuses completely with the. Fig. 10. Spelei'pes bislineatus, larva 43 mm. long. C, arteria carotis interna; , canalis lateralis; , cavum perilymphaticum; , fenestral plate; L., lagena; M., musculus cephalo-clorso-mandibiilaris. ear capsule, leaving the foramen free. Here it is found that, while there is a slight cutting out of the operculum from the ear capsule, it results largely from a gi-owth of the cartilage cephalad into the fen- estral membrane. The situation in the Plethodontidse differs from either of these. The columella, when first coming into intimate rela- tion with the ear-capsule, is small as compared with the size of the for-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsbury, Benjamin Freeman, 1872-1946; Reed, H. D.
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