Calcified Hyoid and Mesopodial Elements of Plethodontid Salamanders

Radiographs of series of Thorius pulmonaris, Parvimolge townsendi, Lineatriton lineolus and various other plethodontids were made with a beryllium-window x-ray machine, using the techniques described by Miller (1957). The radiographs were examined for x-ray opaque areas in the hyoid and mesopodials. Opaque hyoid elements were easily detected. Most of the available specimens of Lineatriton and Parvimolge were not preserved in positions convenient for x-ray study of the limbs, and the number of x-ray opaque mesopodials in them could not be determined accurately. The series of Thorius, however, was preserved with the trunk straight and the limbs at right angles to the body, and in these the number of opaque mesopodials could be counted. In order to verify the radiographic determinations of ossified or calcified mesopodials, three of the x-rayed specimens of Thorius pulmonaris were cleared and stained with alizarin red S. One, a large adult female (26.9 mm.), had the maximum number of x-ray opaque mesopodials observed in Thorius; a second female (24.5 mm.) had an intermediate number; a third female (23.4 mm.) was the largest that had no opaque mesopodials. In each of these the number of elements that stained with alizarin agrees with the number that were x-ray opaque. It is felt, therefore, that the use of x-rays to determine the presence or absence of ossifications or calcifications is justified, and that the results obtained are consistent with those that would be ob-