On the Nerve Supply of Trachea, Bronchus and Lung in Goat

Abstract

A few specially mentionable findings on the histology of the respiratory tract of goat are given in the following:In the trachea, a circular smooth muscle layer lies inside of the tracheal glands, in the portion where the paries membranaceus is formed. This muscle layer becomes better developed distalwards and in the distal end part, comes to cover the nearly complete circumference of the trachea outside its mucous membrane. The right and left extrapulmonary bronchi, very short ducts soon replaced by large intrapulmonary bronchial branches, have a fine structure similar to that of the distal end of the trachea, except that the cartilages are circularly divided into many pieces and are arranged intermittently or in 2 or 3 layers.In the small bronchial branches ca. 2mm in diameter, the cartilaginous pieces are reduced both in number and in size, so weak longitudinal mucous folds come into formation and the bronchial glands also decrease abruptly. In the smaller bronchial branches ca. 1mm in diameter, more prominent longitudinal mucous folds are formed and the epithelium becomes a 2-3-rowed ciliated one, but the muscle layer is yet perceptibly developed. In the bronchioli terminales, the epithelium is composed of one layer of ciliated cells and outside the propria, a circular muscle layer is still visible. The bronchioli respiratorii are lined by a one-rowed nonciliated cylindrical epithelium and a small quantity of muscle tissue. Nothing mentionworthy was found in the alveolar ducts or the alveolar sacs.As in the human trachea (HAYASHI), sensory fibres and their terminations derived from the n. vagus are found in the trachea of goat too, but in the latter, their number and size are smaller than in man. The thick medullated sensory fibres end in branced terminations in the muscle layer, but never forming end-plates as seen in man. Their form, however, suggests the possibility that they are so many Type I terminations concerned with the reflex of lowering the blood pressure. The thin medullated fibres run into the propria and end subepithelially in unbranched and simple branched terminations, only a very few running further into the epithelium. In goat's trachea, no such branched intraepithelial terminations as found in the human counterpart were ever found.As in man and other mammals, in goat too, primary, secondary and tertiary plexus are formed in the interpulmonary bronchial branches, though somewhat poorer in development. In the muscle layer are found branched terminations originating in thick myelinated fibres, while in the propria mucosae are seen some unbranched and simple branched terminations formed by thin myelinated fibres. No intraepithelial fibres are found here. The above findings are rather similar to those obtained in dog (SAITO), but the terminations are somewhat poorer in development than those in dog's bronchus and major bronchial branches.Sensory fibres and their terminations are found in the small bronchial branches and even in the bronchioli of goat too, as it was the case with dog (SAITO) and bat (NUMATA). As in dog, these are better developed than in the larger bronchial branches. The sensory fibres are rather large both in number and in size and simple branched terminations are also found here and there, beside the unbranched ones.What is of interest, unbranched and simple branched terminations formed by rather thick medullated fibres are found also in the interalveolar septa of goat, as in those of bat, in a somewhat better development than in the latter.In the interlobular connective tissue of the lung of goat, nerve bundles containing many thick medullated fibres are found running in company with small pulmonary veins. These bundles run further to reach finally the pleura visceralis. The sensory fibres, as in bat, probably end in unbranched or simple branched terminations in the pleura, but I regret I failed in adequately ascertaining their terminal mode.