Innervation especially sensory innervation of dog tongue.

Abstract

There is no essential histological difference between the motor end plates in the tongue of dog and that of man. In the former, as well in the latter, the Boeke's accessory fibres are not of sympathetic but of motor nature. In the canine tongue, few if any muscle spindles are found. The nerve cells found in many places on the nerve bundles running through the tongue muscles and gland parenchyma, the Remak's hemiganglion cells in the basal plexus in the foliate and cirumvallate papillae and the sporadically occurring nerve cells in tela sumbucosa are all small and degenerative, but are multipolar and must be of sympathetic nature. The termination of vegetative fibres in dog tongue is also represented by the terminalreticulum. The filiform papillae are much smaller in scale than by man, showing low cylindrical form containing 2 or 3 secondary papillae, with very weak cornified surface of epithelium. The sensory fibres thereto are correspondingly very few in number, and the terminations are in general of simple unbranched or branched type consisting of medium or small size fibres, but frequently of larger fibres showing change of size. No intraepithelial fibres are found to exist. Corpusclar terminations as seen in man also are lacking. The fungiform papillae are small at the fore part of the tongue but larger at the hinder part, with secondary papillae. In the epithelium taste buds are often observed. The innervation is weak in the fore part, but as we go backward, the nerves become better developed, with frequent formation of basal plexus at the base. The sensory fibres originating in it run into the papillae, to pass into simple branched and unbranched or more complex plexuslike terminations. But also here, no corpuslcar terminations may be seen. But as the epithelium is covered by the corneous plate, formation of intraepithelial fibres may be observed, though in a weak development. The development of gustatory fibres to the taste buds is also poor, most of them being out of direct supply of intra- and extragemmal fibres. In the canine foliate and circumvallate papillae, many taste buds exist not only in the epithelium facing the grooves but also in that facing the mouth cavity. But in the epithelium of the wall surrounding the circumvallate papillae, the existence of taste buds is very limited. At the base of these two kinds of papillae, conspicuous formation of basal plexus is seen, and the sensory fibres originating in it are better developed than in filiform and fungiform papillae, forming terminations of various forms under the epithelium. Simple unbranched terminations are little in number, branched terminations being prevalent. Branched terminations are further divided into simple and complex forms, the latter again into arborized and plexus-like terminations showing change in size and peculiar winding course of the fibres. The development of sensory fibres to the taste buds in these papillae is rather good, but glomerular terminations observable in man cannot be found, only simple quasi-glomerular bodies being formed rarely in the foliate papillae. However, similarly to the human counterparts, looplike, plexus-like and other simple branched terminations are not lacking under the taste buds here. Intra- and extragemmal fibres often run into or around the taste buds, but these are generally unbranched, ending sharply, never in knob-like nor lamellar bodies. As many of these taste buds are observed without any direct supply of sensory fibres, it may be concluded that the development of the gustatory fibres is much inferior in dog tongue than by human being.