Abstract
D.Sc. (Zoology)
The development of the chondrocranium, including the procartilaginous as well as some mesenchymatous developmental stages, was described in the chinese grass carp, ctenopharyngodon idella (Val.). Fourteen developmental stages, ranging from 5,0 mm to 11,0 mm, were microtomized, stained with Heidenhain's azan solution, mounted and examined. Seven developmental stages were described using drawings and reconstructions made from frontal, sagittal and transverse sections. The ontogenesis of the skeletal structures in the ethmoidal, orbitotemporal and otico-occipital regions of the neurocranium was investigated. Special attention was given to the development of the cranial muscles as well as to the ontogenesis of the skeletal structures of the viscerocranium. The lamina precerebralis-, noticed in other cyprinids as well as in the siluroids, was regarded as the morphological anterior wall of the brain capsule and the posterior part of the nasal septum as the morphological posterior wall of the nasal capsule, greatly reduced in Teleosts. The lamina orbitonasalis represents a supra-pharyngopremandibular. In the orbitotemporal region the cartilaginous trabecula and polar cartilage are initially separated by a procartilaginous bridge which forms the side-wall of the carotid incisure. A pila lateralis is absent in Ctenopharyngodon idella. The prootic, chondrifies intramembranously, a fact which supports Bjerring's(1977) view that the otic capsules are derived from the dermatomes. The composition of the palatoquadrate and of the hyomandibular in elasmobranchs and teleosts are discussed. The development of the internal and external derivatives of the dorsal constrictors of the branchial arches were
investigated and their possible homoloques in the prootic visceral arches discussed. The levator and adductor muscles of the opercle probably represent a modified
musculus adductor arcus hyoidei.