Comparison of the anatomy of the eustachian tube in the rhesus monkey (Macaca mulatta) and man: implications for physiologic modeling.

The primate nasopharynx-eustachian tube-middle ear complex is being used to model both the normal and pathologic functions of the human eustachian tube by several researchers. An extensive search of the literature has indicated little detailed information on the primate eustachian tube/middle ear system. This study was undertaken to define the anatomical characteristic of the system in the Rhesus monkey (Macaca mulatta) and to determine the limits on the use of the monkey as a model of human eustachian tube function. Although the direct application of morphologic data to explain the function of a system is tenuous, the data on the Rhesus monkey eustachian tube appears to be consistent with that published for other mammals. The tensor veli palatni muscle appears to be the only muscle to act directly on the tube and effect tubal dilation. The muscle is attached to the lateral membranous tubal wall along its extrabullar extension. The muscle has an inferior attachment to the posterior hard palate and thus possesses a vector directed inferolaterally; contraction would appear to pull the membranous wall inferiorly and laterally, resulting in the tubal dilation. The eustachian tube relationships of the salpingopharyngeus, levator veli palatini, and internal pterygoid muscles are described. Their possible role in primate tubal function is minimal at best.