Rat eustachian tube and its musculature

The objective of this study was to evaluate the anatomy of the eustachian t ube (ET) of the rat and the paratubal musculature. Microdissection and seri al sections were used. The ET consists of collapsible membranous and membra nocartilaginous segments and a noncollapsible bony segment. Tubal muscles a re attached to the collapsible part; the salpingopharyngeus muscle (SPM) is well developed and consists of 3 distinct groups of muscle fibers; the ten sor veli palatini muscle (TVPM) consists of 2 functionally different groups of fibers, but only 1 group assists in opening the ET. Attachment of the f ibers of the SPM and TVPM that are involved in tubal opening is confined to the dorsal portion of the ET This finding, together with the earlier obser vation that this part is mainly lined by squamous epithelium, strongly sugg ests that the dorsal part has a ventilatory function. The ventral portion o f the ET, which is lined by ciliated-secretory epithelium and lacks the att achment of muscle fibers that can dilate the lumen, is assumed to serve cle arance. The anatomic position of the levator veli palatini muscle suggests that this muscle contributes to the protective function of the ET. These fi ndings are discussed with regard to the ET in humans.