The results of my study on the histology and the innervation of the nasal cavity and the snout of 4 and 5 month cattle fetus may be summarized as follows.
The structure of the snout is specific in that the epithelium covering it is a thick bladder-like epithelium, very large papillae being grown into it from the propria, and that the submucosa contains very well-developed snout glands, of which the ducts run out through the papillae. The snout has on the other hand sinus hairs growing on the lateral side, so that it must in a part originate in haired skiu, too.
The proper nerves supplied to the snout are surprisingly well developed and show formation of plexus submucosus, plexus laminae propriae and intrapapillar plexus. These plexuses are composed of many thick sensory fibres and a few fine vegetative fibres, the latter coming into anastomosis with the perivascular plexus. The terminations of the vegetative fibres here also form STÖHR's terminal reticula, which are particularly well developed around the snout glands and the blood vessels and stand in control over various tissue cells by direct contact.
The sensory terminations found in the snout are of branched type formed subepithelially, but a part of the sensory fibres form intraepithelial fibres. The subepithelial terminations are always of simple branched type, and the terminal fibres show frequent change in size, to end in sharp or sometimes in blunt points. The intraepithelial fibres comprise both fine and thick ones, of which the fomer mostly run simple courses, but the latter run looping courses, often showing simple glomerular arrangement. The intraepithelial fibres are usually of unbranched type, but branched ones are not rare, either.
Near the orifice of the vestibulum nasi, there is a special area with vibrissae growing on it. This part probably corresponds to the pars cutanea in the human nose, but in bovine fetus it does not belong to the haired skin, but together with the snout to the mucous membrane, for its epithelium is 2-3-folds thick as the epidermis and is nothing different from the stratified flat epithelium of the vestibulum nasi of the other parts. It is a part of specific haired mucosa.
The vestibulum nasi, outside this specific haired mucous part, is lined near the orifice by a horn-plated hornified mucous membrane, then to the back, by a nonhornified mucous membrane nearer the pars respiratoria, where the epithelium becomes thinner. Then comes a transitional part covered by a 4-5-rowed cylindrical epithelium and more backwards the pars respiratoria covered by a 2-3-rowed ciliated epithelium. In the hornified mucosal part the papillae are in good development but they become poorer backwards and in the next non-hornified mucosal part, they are no more to be found. The nasal glands come into appearance in cat and dog only in the deep part of the vestibulum nasi, but in cattle they are found all over the vestibular wall. The pars respiratoria has nasal glands and venous plexus in its subepithelial connective tissue, as in cat and dog.
The sensory innervation of the specific haired mucous part of the vestibulum nasi is very powerful as in the case of the snout of the same nature. A part of the sensory fibres in the well-developed nerve plexus formed in the submucosa containing hair roots form plexus-like terminations in the SETO's so-called hair-nerve shields or tubes quite as in common haired skin. The remainder of the fibres, unlike in common haired skin, run further into the propria and end in branched terminations. Their terminal fibres sometimes run further into the epithelium to end as short intraepithelial fibres.
The sensory innervation of the vestibulum nasi in general is better in cattle fetus than in man. The nearer to the orifice, the part is the better provided with sensory fibres and their terminations, and when we go over the transitional part into the pars respiratoria, the innervation becomes rapidly poorer.
View full abstract