Histological Study on the Nerve Distribution in the Larynx in Cat

Abstract

The r. internus of the n. laryngeus superior comiug into the cat's larynx runs through the canal found in the lateral mid-part of the thyroid cartilage and then divides into the ascending and the descending rami, the latter forming the r. communicans communicating with the n. laryngeus inferior and the former, the thicker of the two rami, parting into bundles of varying sizes which run upwards mostly toward the laryngeal side of the epiglottis and partly to the posterior portion of the plica vocalis, whence some finer branches are sent out to the upper portion of the cavum laryngis inferior. These nerve fibres comprise fine vegetative fibres as well as thick sensory fibres and contain large and small ganglia of sympathetic nature in their courses. The sensory fibres contained in the r. communicans finally spread out in the mucous membrane of the cavum laryngis inferior.
The n. laryngeus inferior also consists of fine vegetative fibres and thick medullated fibres and accompanying small ganglia in their upward courses passing between the thyroid cartilage and the m. cricothyreoideus, sends out many branches into the laryngeal muscles and besides also a few fine branches composed of vegetative and sensory fibres into the mucous membrane in the lower part of the cavum laryngis inferior.
In the laryngeal side of the epiglottis the submucosal and the proprial plexus are very well developed and consequently, this part is best supplied with sensory fibres of all the parts of the laryngeal cavity. Their terminations, however, are somewhat simpler than the same in dog and goat, consisting only of simple branched terminations originated in medium-sized fibres. These terminations, unlike those in man and some animals, rarely end subepithelially, their terminal fibres usually ending in intraepithelial fibres. These terminal fibres are rarely formed of thick fibres as in dog and goat but are usually very fine fibres provided with small knobs, mostly ending sharply or in small knobs in the snperficial layer of the epithelium.
The area the second richest in sensory fibres next to the epiglottis is the part of the mucous membrane covering the apex of the arytenoid cartilage behind the plica vocalis. In the mucous membrane of the ventriculus laryngis are found 2 or 3 papillae resembling the taste-budded papillae on the tongue and many sensory fibres run into these papillae too. The thin mucous membrane covering the arytenoid cartilage extending downwards from the rima glottidis is also considerably rich in sensory fibres. The largest part of the plica vocalis except its posterior portion and the mucous membrane of the cavum laryngis inferior adjacent to it are very poor in sensory fibres.
The sensory terminations in the dorsal portion of the plica vocalis, somewhat unlike those in the epiglottis, consist more often in subepithelial rather than intraepithelial terminations of simple branched type, of which the terminal fibres slowly taper off into sharp points. The few intraepithelial fibres are formed by fine fibres or sometimes by medium sized fibres nearly devoid of knobs and rarely go up as far as to the superficial layer of the epithelium. The thin mucous membrane covering the arytenoid cartilage in the cavum laryngis inferior also contains rather many simple branched subepithelial and intraepithelial terminations closely resembling those in the posterior portion of the plica vocalis.
The part of the mucous membrane beneath the ciliated epithelium in the cavum laryngis inferior shows a very inferior development of the proprial plexus and consequently the sensory fibres here are very small in number. These fibres end in unbranched and simple branched sub- and intraepithelial terminations composed of very fine terminal fibres devoid of knobs.
The taste-buds in the cat's larynx are as abundant as in the dog's and goat's larynges, particularly so in the laryngeal side of the epiglottis