Otogenesis In The Fetus Of Sheep Ovis Aries

Abstract

The present study was undertaken to elucidate the developmental changes in ear. The study was conducted on 60 embryos and fetuses of Nellore sheep between 22 to 145 gestational days. Morphogenesis revealed that five aural hillocks appeared at 23 days fused to form the pinna later. External acoustic meatus (EAM) appeared first at 24 days. Hairs were apparent on EAM by 126 days. Pinna was pendulous and elongated at 145 days. Tympanic cavity presented three tiny ossicles malleus, incus and stapes at the epitympanic region by 63 days. Rostral process of malleus and Lenticular bone were absent in sheep. The ossified part of tympanic ring appeared in semi lunar shape by 55 days. Ossification initiated in vestibule and cochlea by 70 days. newlineHistogenesis revealed small cone shaped pinna at 24 days. Pharyngeal cleft modified into EAM by 39 days and canalized by 49 days. Epithelium of pinna was keratinized at 99 days. The meatal plug appeared first in 24 day embryos and formed primary external auditory canal (EAC) between 31 to 39 days. The ceruminous and sebaceous glands were first identified by 80 days. Middle fibrous layer of ear drum was formed at 126 days. Tympanic membrane appeared trilaminar and EAC was completely canalized by 140 days. Meckel s and Reichert s cartilages developed as mesenchymal condensation by 23 days. The distal part of Meckel s cartilage modified into malleus and incus. Blastemal cells of Reichert s cartilage modified as stapes. Tubo tympanic recess (TTR) differentiated between 24 to 27 days. Ossification initiated in malleus, incus and stapes at 63, 78 and 80 days respectively. Incudo-malleal and incudo-stapedial joints were established as diarthrodial joints by 80 and 85 days respectively. Eustachian tube lined by psedostratified ciliated columnar epithelium and Meckel s cartilage disappeared by 85 days. Ossicular ligaments were differentiated at 104 days. The tympanic cavity comprised of fully grown ossified ossicles as adult by 140 days. newlineOtic placode of inner ear differentiated into the otocy