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* Department of Zoology, Faculty of Science, Ain Shams University, Abbasiya, Cairo, Egypt+ Department of Zoology, Zagazig University, Zagazig, Egypt

ABSTRACT

The ontogeny of the mandibular arch of the teleost fish, Gambusia affinis affinis is studied in six developmental stages and compared with that of other bony fishes. The mandibular arch is composed of the palatoquadrate and Meckels cartilage; the two elements appear earlier during ontogeny as independent structures in a procartilaginous state. The pterygoid part of the palatoquadrate develops as an anterior outgrowth from the quadrate part in the 4 mm larval stage. The palatoquadrate articulates with the ethmoid plate of the chondral neurocranium by an ethmopalatine articulation in the 6 mm stage. Meckels cartilage first appears at the 3.5 mm stage anteriorly, separate from its fellow of the opposite side. At the 5 mm larval stage the two Meckels cartilages connect with each other. At the 6 mm larval stage the posterior end of each cartilage is differentiated into two processes; the coronoid and retroarticular processes. The palatoquadrate articulates with Meckels cartilage between these two processes.