The progress of ossification of the skull of the American toad
Toads were raised in the laboratory from the egg stage through three weeks after foreleg emergence. Three to six toads were preserved from each of ten stages of development between stage XX (foreleg emergence) and three weeks after stage XX. The specimens were cleared and stained by the alizarin technique, examined under a binocular dissecting microscope, and the skull bones drawn freehand.At stage XX ossification had begun in the frontoparietals, parasphenoid, premaxillae, septomaxillae, prootics, and exoccipitals. By one day after stage XX the squamosals, dentaries, and angulosplenials had appeared; by two days, the nasals and maxillae. By three days, two of four specimens possessed two ossification centers of each titerygoid bone. At three weeks the beginnings of the hyoid apparatus were apparent.Comparisons were made to the ossification of skull bones reported in the literature for Pseudacris triseriata and Rana pipiens.