THE DEVELOPMENT OF THE SKULL OF GAMBUSIA-AFFINIS-AFFINIS (BAIRD AND GIRARD) .3. THE DEVELOPMENT OF THE HYOID ARCH

The development of the hyoid arch of six postembryonic stages of Gambusia affinis affinis (3.5, 4, 5, 6, 8 and 10 mm total length) is described from serial cross sections and graphical reconstructions and compared with that of other fishes. The study has revealed that the different constituents of the hyoid arch, viz. the hyosymplectic, interhyal, ceratohyal, hypohyal and basihyal are developed as independent structures during ontogeny. In the 10 mm stage, absorption of cartilage with replacement by bone is observed at the level of the hyosymplectic and ceratohyal. The hyosymplecitc chondrifies as a single structure and, later on, during ontogeny, it divides due to the absorption of cartilage into two parts; the hyomandibular and symplectic process. The hyosymplectic part of the hyoid arch plays an essential role in jaw suspension, so that Gambusia affinis affinis, like the majority of Selachi and all Teleostei, conforms to the hyostylic type of jaw suspension.