Sensory Innervation of Dorsum Linguae in Goat

Abstract

The filiform papillae of the dorsum linguae of goat are far poorer in development than in man, are covered by stratified epithelium with horn-teeth, have narrow stems and only very poorly developed secondary papillae. The sensory nerve fibres innervating them, therefore, are very poor in number and their terminations are represented only by unbranched or simple branched terminations and none of the terminal fibres running so far as into the secondary papillae.Numerous specific large papillae are found paving the tongue surface posterior to the transverse furrow of the middle portion of the dorsum linguae. These papillae are of flat cylindrical form, have very thick epithelia, show incomplete hornification of the surface and have many elongated secondary papillae growing out of the comparatively well-developed papillar stems. These specific papillae come to resemble closer the filiform papillae in structure as we go the more lateralwards and finally pass over into genuine filiform papillae. The development of sensory fibres in these specific papillae is very poor, as in the filiform papillae, so that they end generally in unbranched or simple branched terminations. Unlike the filiform papillae, however, these large papillae often contain unbranched terminations ending deep in the secondary papillae, and even in the epithelium forming intraepithelial fibres. Such a better innervation is possible as these specific papillae are better developed than the filiform papillae.The fungiform papillae of goat are not essentially different from those on the human tongue, and are accordingly far better innervated sensorily than the above filiform papillae. A large number of sensory fibres are found running into their stems and ending subepithelially in branched terminations therein. Comparatively complex branched terminations are not rare here. A small number of unbranched intraepithelial fibres are also observed.Taste-buds are often formed in the epithelium facing the oral cavity of the fungiform papillae, especially often in the papillae in the tip part of the dorsum linguae. The sensory fibres supplied to these taste-buds, however, are rather poor in development, some taste-buds devoid of any sensory innervation being found in many places. The sensory fibres, where presnt, usually end in branched terminations directly beneath the taste-buds, but not rarely some of them run further to form intra- and extragemmal fibres.Not only in the above lingual papillae, but also we often find unbranched and simple branched terminations formed in the propria of the mucous membrane, particularly often close beneath the epithelium.Finally, it is very intereresting that not rarely some very specific simple endbodies are found in the lamina propria as well as the various lingual papillae of the goat dorsum linguae. This end-body, encased in a thin connective tissue capsule, consists of an outer light zone and an inner bulb, which contain numerous special cell nuclei resembling SCHWANN's nuclei in nature. These nuclei are particularly abundant in the inner bulb. One or sometimes two myelinated sensory fibres run into the inner bulb and sometimes form club-like terminations therein by gradual fibrillar swelling or simple branched terminations. These specific end-bodies are specific to non-human mammals and probably represent receptors of very delicate feelings, as are the human complex sensory end-bodies.