It is generally accepted that the air pressure in the middle ear cavity is regulated by the Fustachian tube. Moreover, it is well known that the opening of the Eustachian tube is brought about by the tensor palati muscle, the lebator palati muscle and the salpingopharyngeus muscle, but there is no complete agreement as yet on the question by what mechanism each of these msucles performs the opening action. With the purpose of elucidating this point, the author studied by the methods mentioned below the relationship between each of these msucles and the Eustachian tube, especially the relatiônship between the tensormuscle and the membranous portion, that between the levator palati muscle and the base of the Eustachian tnbe and alse the question as to whethet or not the salpingopharyngeus msucle can function independently. 1. Macroscopic observations; Using six autopsy specimens containing the tensor palatini muscle, the levator palatini muscle and the salpingpharyngeus muscle which were taken from the right side only and fixed in a 10% formalin solution, the author explored muscle fiber ends of each by magnifying them threefold with a loupe. 2. Histological oaservations; In six autopsy cases other than the above-mentioned, their tissues surrounding the Eustachian tube and tube and tubal muscles are removed and fixed in a 10% formalin solution and decalcified, embedded in paraffin, and than sliced at a right angle to the axis of the tube into serial sections 25U thick. After hematoxylin-eosin staining the author studied hsitologically the relationship between the tunal cartilage, membranous portion and tubal muscles. The following are the results. a. Tensor muscle. It is sometimes possible to divide the tensor msucle into the anterior, middle and posterior parts, ans the muscle fibers are abundant in the middle part. Commonly the source of this muscle is found in the skull base and in the lateral cartilaginous lamina, but in some instances this muscle originates in the middle portion of the muscle at the membranous portion near the lateral cartilginous lamina. The other portions of the tensor muscle appear to be connected with the membranous portion only by connective tissue. The density of the connection differs in individual cases, and moreover, in some cases they can be readily separrted while in others they are compactly connected with one anoeher. b. Levator muscle. This muscle generally runs parallel with the longitudinal acis of the tube under the base of the Eustachian tnbe, ane some send out several muscle fibers from the inferior part of the mucous membrane of the tube. In some instatces muecle fibers are observed originating from the inferior terminal of the medial carti agenous lamina and inferior exterior side of the tube.
Moreover, the relationship betwee tensor muscle and tubal base differs according to the construction of the tubal cartilage. Namely, in the shape generally know, the levator muscle adheres to the base of the tube for its whole length, and in the case where the inferior terminal of the tubal medial cartilagenous lamina is running around the exterior side like lateral lamina (the author designates this as type II distinguishing it from the cartilage of the generally-Know shape which is designated as type I) and in the case where by the presence of auxiliary cartilage the cartilage presents a shape similar to type II, it is obvious that cartilage exists between the levator muscle and the base of the tube. c. Salpingopharyngeus muscle. In some cases muscle fibers are lacking in the salpingopharyngeus muscle, and even in those having muscle fibers, the number of such fibers is small, occupying only a portion of the salpingopharyngeal fold.