The development of the chondrocranium of Gallus gallus.

Abstract

An account of six stages of the development of the chondrocranium up to the beginning of ossification is given. The tip of the chorda does not pierce the anterior surface of the acrochordal in the early stages and the fenestra basicranialis posterior develops through resorption of the basal plate. The posterior part of the orbital cartilage develops a laterally situated orbitocapsular commissure and a medially situated pila antotica spuria. The pila antotica is resorbed leaving the posterior orbital cartilage connected to the basal plate only by the pila antotica spuria. In the earliest stage the cochlear portion of the otic capsule is fused to the basal plate, but can be distinguished from the basal plate and the canalicular portion. The tectum synoticum is attached to the otic capsule by two roots with the ventral attachment spreading over the lateral surface of the pila occipitalis. The trabecula communis forms without the intervention of an intertrabecula. The interorbital and nasal septa develop from the trabecula communis. An ethmoid plate forms the roof of the nasal capsule and the rest of the capsule develops as outgrowths from the roof. A transitory floor for the posterior part of the nasal capsule is present in the young stages and an incomplete floor for the anterior part develops late during the ontogeny.