In spite of numerous investigations of the laryngeal nerves, there is no complete agreement as to the innervation of the laryngeal nerves. This study was carried out to elucidate the problems of the larynx innervation, especially to illustrate the motor nerve supply to the laryngeal muscles of mammals. Three methods were chosen for this study.
a) Dissection of excised larynges under a binocular microscope without staining. Twenty-five human larynges, ten larynges of the dog, cat, rabbit, goat, sheep, horse, cow and pig respectively were employed in this investigation.
b) Dissection of larynges, in which the nerves were supravitaly stained with methylen blue. Five dogs, five cats and ten rabbits were employed in this observation.
c) Histological examination of the Galen's anastomosis after the superior or inferior laryngeal nerve was resected. This experiment was planned in order to illustrate whether the Glen's anastomosis is composed of superior laryngeal nerve or inferior nerve. Four dogs, the superior or inferior laryngeal nerve of which had been disscted before one month, were studied.
The results were summarized as follows:
1) In all cases of man, dog, horse, sheep, goat and pig, the internal branch of the superior laryngeal nerve entered into the larynx penetrating the thyrohyoid membrane except one human case in which the nerve penetrated the thyroid cartilage at the thyroid foramen such as observed in all cases of cat, rabbit and cow.
2) The internal branch of the superior laryngeal nerve was divided into three main branches after penetrating the thyrohyoid membrane: Ramus anterior, media et posterior. In man and dog the site of division showed individual difference. In man the type of the intralaryngeal division was most frequently found, on the contrary the extralaryngeal division was most frequent in dog. In the other mammals the internal branch was divided after it entered into the larynx except one case of rabbit.
3) The epiglottis was innervated mainly by Ramus anterior in mammals: however, in horse and cow, whose epiglottis was comparatively large, it was observed that Ramus media as well as Ramus anterior supplied the sensory nerve to the mucosa of epiglottis.
4) The aryepiglottic fold and laryngeal vestibule were innervated by R. media: however, the subglottic space was never.
5) The arytenoid region was innervated chiefly by Ramus posterior: i. e., some twigs of Ramus posterior pierced the arytenoid muscle and supplied the sensory nerve to the inner surface of the arytenoid cartilage, and some of the others anastomosed with twigs of the inferior laryngeal nerve in the arytenoid muscle. These twigs of the inferior laryngeal nerve have been considered to innervate the arytenoid muscle, however it was not illustrated in this study whether the superior laryngeal nerve supplies a motor nerve to the arytenoid muscle or not.
6) Galen's anastomosis consisted of R. posterior of the internal branch of the superior laryngeal nerve and R. posterior of the inferior laryngeal nerve. Galen's anastomosis was very small in all cases of pig and was not occasionally found in some specimens of horse.
7) The external branch of the superior laryngeal nerve innervated the cricothyroid muscle in every mammal.
8) The inferior laryngeal nerve was fouud to be divided into two main branches before it entered into the larynx in many cases of mammals, except pig and few cases of man, cat and dog.
9) R. anterior of the inferior laryngeal nerve innervated the homolateral posterior cricoarytenoid, arytenoid, lateral cricoarytenoid and thyroarytenoid muscles in every mammal, however, in man and cat, the arytenoid muscle was double innervated by bilateral inferior laryngeal nerves. Ramus posterior composed Galen's amastomosis with a branch of the superior laryngeal nerve.
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