On Histology and Sensory Nerve Supply of Larynx in Flying-squirrel

Abstract

The epithelium of the laryngeal side of the epiglottis of flying-squirrel is a stratified flat epithelium much thinner than that on its lingual side, but near its median line, it is a 5-6-rowed ciliatated epithelium. No papillae are formed beneath this stratified flat epithelium, as are found on the lingual side of the epiglottis. Taste-buds are found on the lingual side alone in small number. The mixed glands are well developed in the median and the peripheral parts of the laryngeal side. The epiglottic cartilage is of hyaline nature and forms one integral plate.The ventriculus laryngis forms a huge laryngeal sac, which reaches the inner surface of the thyroid cartilage on the ventral side, juts out toward the pharyngeal mucous membrane on the dorsal side, reaches the vicinity of the hyoid bone beyond the upper border of the thyroid cartilage on the cranial side and extends down to the upper end of the trachea on the caudal side. The sac is generally lined by a one-rowed cubic epithelium and partly by a 2-rowed cylindrical epithelium. The propria is very ill developed and mixed glands are found only in a limited area.The vocal cord consists in the main of 2-rowed stratified flat epithelium and a thin propria, but their ventralmost part alone is covered by a 2-3-rowed cylindrical or ciliated epithelium. The ventral one-third of the pars intercartilaginea of the rima glottidis is composed of a 2-rowed flat epithelium and a thin propria, but its dorsal tow-thirds are of a 2-3-rowed ciliated epithelium and subepithelial connective tissue gradually gaining in thickness dorsalwards and containing some mixed glands. The lower part of the larynx between the rima glottidis and the entrance to the trachea is composed of a 2-3-rowed ciliated epithelium and a subepithelial connective tissue layer containing mixed glands.The laryngeal mucous membrane of flying-squirrel is supplied with sensory fibres as in man, dog, goat and rabbit, but much less abundantly than in these, the submucosal and the proprial plexus found very well developed in these mammals being much inferior in flying-squirrel. The sensory nerve terminations are also much simpler in formation, no such corpuscular terminations or complex branched terminations as found in the above animals being ever to be found here.The sensory terminations found in the laryngeal mucous membrane of flying-squirrel are of unbranched and simple branched types formed either subepithelially or intraepithelially. Most primitive subepithelial unbranched terminations are found everywhere in the mucous membrane and in the laryngeal sac in particular most of the terminations are of this type, found here and there in sporadic existence. Thus, the sensory supply to the laryngeal sac may be called very poor in general, but near the entrance of the ventriculus laryngis subepithelial and intraepithelial simple branched terminations are not rare either. The terminal fibres of these terminations are sometimes comparatively thick and sometimes run wavy courses.The laryngeal side of the epiglottis is richest in sensory fibres, rather complex branched ones being found among their terminations, especially near its median line. Branched terminations with several terminal fibres are not rare here and some complex intraepithelial branched terminations are present, but the terminal fibres are usually medium-sized or thin, showing not much change in size. In the peripheral parts of the laryngeal side of the epiglottis, the sensory fibers are fewer and their terminations are simpler, but in these parts, simple brached terminations originating in thick fibres may be observed. Terminations formed by extraordinarily thick fibres, as found in man and rabbit, are never found in flying-squirrel.Sensory terminations are found on the border part between the laryngeal and the lingual sides of the epiglottis but their number decreases rapidly as we pass over into the lingual side