Hyoid Arch of Rhinobatidæ

Abstract

THE skeleton of the hyoid arch of Batoidei has been for many years the subject of discussion by morphologists. Gegenbaur¹ considered the hyoid elements bearing hyal rays and lying posterior to the hyomandibular cartilage to represent the ceratohyal of Selachoidei, which became disconnected from the ventral edge of the hyomandibular and extended upwards behind it. Krivetski² and de Beer³ considered these hyoid elements as pseudohyoid and formed by the fusion of the proximal ends of the hyal rays. Such a phenomenon occurred during the phylogenetic divergence between Batoidei and Selachoidei, and was largely associated with the increased distance between the mouth and first gill slit in Batoidei. Thus the pseudohyoid elements were necessary for providing a support for the hyal rays, as well as the anterior wall of the first gill slit. During the enlargement and extension of these pseudohyoid elements, the original ceratohyal in Batoidei has disappeared.