On Sensory Innervation of Larynx in Dog

Abstract

The mucous membrane of larynx in dog is smaller and simpler than in man in scale. The epithelium is either stratified flat or multi-lined ciliated, the major part of larynx being covered by the former and pars intercartilaginea and pars inferior laryngis only being surfaced by the latter type of epithelium. The height of epithelium is lower than that of man. These facts suggest the lower stage of development of nerves, especially sensory nerves in this part, in dog than in man.
The nerves supplyint the laryngeal mucous membrane are originated in n. laryngicus cranialis of n. vagus and truncus sympathicus cervicalis. The former consists-of thick sensory fibres and fine parasympathetic fibres, which divide into small bundles upon reaching to basis of epiglottis.
The majority of nerves for epiglottis run over the laryngeal side, only a small minority going to the pharyngeal side. The former penetrate the small pores of cartilago epiglottidis and pass into plexus submucosus and plexus tunicae propriae, latter also pass into both plexus, but their development is very inferior. These plexuses are much more backward in development than those in adult human larynx (Sasaki), resembling more those in tenth month embryo (Momono).
The nerves for the extraepiglottid mucous membrane of larynx are less well-developed than those for epiglottis, but they may be called rather strong only in plica ventricularis and pars intercartilaginea, being poor in ventriculus laryngis and pars inferior laryngis and extremely poor in pars intermembranacea.
As in man, the epiglottis is best provided with sensory fibres in the whole area of larynx. Yet their development is far below that of human larynx. Firstly, in man, both the Types I and II of sensory terminations related with Hering's blood pressure falling reflex are formed conspicuously, in dog, only the simpler Type II is observed. Sencondly, in man, the existence of complex corpursclar terminations is clarified, whereas in dog, only a few very simple non-capsulated glomerular terminations are observed. This situation is much in similarity with the larynx in tenth month human embryo.
Thus, the sensory terminations in the mucous membrane of canine larynx are mostly represented by simplest unbranched and simple branched terminations. However, more complex branched terminations, such as plexus-like terminations are also observed, though in a small quantity. They are generally composed of thick fibres showing peculiar change in size and winding course.
Besides, intraepithelial fibres are demonstrated. They are lower in development than in human adult, but very remarkable on the laryngeal side. Their terminal formation, however, is more similar to those in tenth month human embryo than those in adult human, and classifiable into three types. The Type I consists of fine fibres, the Type II of thick fibres with frequent change in size and the Type III represents an intermediary form of the two former. All of them are again divisible into unbranched and branched terminations. These fibres run in the epithelium very irregularly, to end finally sharply or bluntly.
Sensory terminations in extraepiglottid area of larynx in dog are also much poorer developed than in adult man, resembling more those of tenth month human embryo. The development of sensory fibres is also here parallel to the development of plexus in subepithelial tissue, being at best in plica ventricularis, next in pars intercartilaginea, poor in ventriculus laryngis and pars inferior laryngis and poorest in pars intermembrananacea.
There are two types of sensory terminations related with H.ering's blood pressure falling reflex in man, but only Type IT terminations are observable in dog, which are formed simpler than in human adult. Corpusclar terminations are found in many places in man, while in dog, only very infantile non-capsulated glomerular terminations are found in plica ventricularis, and in no other parts.