The stapedius muscle of the squirrel monkey

Abstract

Contraction of the stapedius muscle (the acoustic reflex) is useful in the clinical diagnosis of various auditory disorders. In an effort to better understand the basic innervation of the acoustic reflex we are presently studying its neuroanatomy in the squirrel monkey (Saimiri sciureus). Since the morphology of the squirrel monkey stapedius muscle (SMSM) has not been previously described, we will present here our own findings from eleven muscles observed under light (LM) and transmission electron microscopy (TEM). Squirrel monkeys were perfused intracardially with either 10% neutral buffered formalin or 3% buffered glutaraldehyde. The stapedius muscles were dissected out under the operating microscope. For LM, the muscles were embedded in JB-4 plastic and cut serially at 5 micra and for TEM, the muscles were processed as previously described (2).The topography of the SMSM in the middle ear is similar to the human (3). The muscle attaches to the posterior side of the stapes' head by a thin collagenous tendon that extends almost midway into the muscle in a postero- ventral direction.