Histological study on innervation of pars mucosa of vestibulum nasi in human embryo.

Abstract

The nasal vestibule is already in good development in the latter stage of the embryonic life, and is divisible, as in adult, primarily into the cutaneous part overgrown with hairs and the mucous part succeeding it on the inner side. In the latter part, however, the distinction of the three parts of the corneal, the noncorneal and the transitional, distinguished by the nature of the epithelium and the formation of papillae, is not yet sufficiently clear. In 6th month embryos, the corneal part is nearly complete, but the non-corneal and transitional parts are both surfaced with thick stratified columnar epithelium, so that their boundary is not clear-cut. In 10th month embryos, the surface of the epithelium in the frontal half of the non-corneal part has changed to stratified flat epithelium, but the rear half remains as yet surfaced with stratified columnar epithelium, and the boundary between the non-corneal and the transitional part remains yet undefined. Papillae are formed in considerable development in the cor-neal part, but almost none in the non-corneal part. The end apparatus of the vegetative nerve fibres is completed as Stohr's terminal-reticulum, and stands in tactile control against the nasal glands, the blood vessels, in particular, the capillaries. There are comparatively few sensory nerve fibres supplying the mucous membrane of the nasal vestibule. Most of the fibres run into the lamina propria and end beneath the epithelium and some run further into the epithelium to end as intraepithelialfibres. As sensory fibres penetrate preferentially into papillae, the corneal part having papillae is provided with better developed sensory fibres than the non-corneal part without papillae. That is, the sensory fibres in the corneal part are generally thick and end in somewhat differentiated terminations, while those.in the non-corneal part are mostly minute and end in simple ones. But these sensory terminations are as yet in much lower stage of development in comparison with those in adult, mostly being represented by the simple unbranched endings, especially in 6th month embryos. The second type of sensory terminations is represented by the simple branched terminations composed of 2-3 rami which are found rather often in the 10th month embryos. The third type of sensory nerve endings is corpuscular in form, but such terminal bodies are as yet not formed in the latter stage of embryonic life. But the terminations showing a very simple glomerular arrangement of sensory fibres, presumably precursors of such bodies, are in some cases found in the major papillae in the corneal part. The fourth type of sensory endings, the intraepithelial fibres, has been proved to exist in the latter embryonic stage, but their infantile form and small number seem to indicate their full-fledged development to be post-poned till after birth. Namely, in 6th month embryo, the intraepithelial fibres are very few in number, are minutely thin and end unbranched after running a short course. In 10th month embryos, these fibres appear with greater incidence, and their terminal mode becomes more complex. For example, in the non-corneal part, there are seen often also bifurcated terminations, and in the corneal part, also branched intraepithelial fibres of medium size. Besides, in both the above parts, many sensory terminal fibres are found touching the basal layer of the epithelium or slightly penetrating it. These fibres probably develop into intraepithelial fibres in post-natal life. Into the strongly developed papillae in the frontal area of the corneal part penetrate stout sensory never fibres to end there sharply or bluntly, but unlike those in adult, none of them has ever been found to run further up into the epithelium, to end as the peculiar thick and short intraepithelial fibre.