Rat eustachian tube and its musculature.

The objective of this study was to evaluate the anatomy of the eustachian tube (ET) of the rat and the paratubal musculature. Microdissection and serial sections were used. The ET consists of collapsible membranous and membranocartilaginous segments and a noncollapsible bony segment. Tubal muscles are attached to the collapsible part; the salpingopharyngeus muscle (SPM) is well developed and consists of 3 distinct groups of muscle fibers; the tensor veli palatini muscle (TVPM) consists of 2 functionally different groups of fibers, but only 1 group assists in opening the ET. Attachment of the fibers 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 observation that this part is mainly lined by squamous epithelium, strongly suggests that the dorsal part has a ventilatory function. The ventral portion of the ET, which is lined by ciliated-secretory epithelium and lacks the attachment of muscle fibers that can dilate the lumen, is assumed to serve clearance. The anatomic position of the levator veli palatini muscle suggests that this muscle contributes to the protective function of the ET. These findings are discussed with regard to the ET in humans.