Welcome back to Hearing International‘s continuing series honoring the Cochlear Explorers, those who first described aspects of cochlear anatomy and physiology that later were named after them. Week XI’s Cochlear Explorer is the only American in the group,  Irving Hardesty  (1866-1944), who considered the tectorial membrane as the vibrating mechanism within the cochlea.

Hardesty’s Membrane

Covering the sulcus spiralis internus and the spiral organ of Corti is the tectorial membrane, which is attached to the limbus laminae spiralis close to the inner edge of the vestibular membrane. The tectorial membrane partially covers the hair cells in the Organ of Corti and vibrate when fluid sound waves hit it.  Its inner part is thin and overlies the topic of last week’s post, the auditory teeth of Huschke.  

Its outer part is thick, and along its lower surface, opposite the inner hair cells, is a clear band, named Henson’s stripe, (for Victor Henson, another cochlear explorer), due to the intercrossing of its fibers.  The lateral margin of the membrane is much thinner.  

The structure known as Hardesty’s membrane divides the subtectorial space into two compartments, one facing the surfaces of inner hair cells and one facing the surfaces of outer hair cells.  It is inconceivably delicate and flexible; far more sensitively flexible in the transverse than in the longitudinal direction and the readiness with which it bends when touched is beyond description.  Ectodermal in origin, it consists of fine colorless fibers embedded in a transparent matrix (the matrix may be a variety of soft keratin) of a soft collagenous, semisolid character with marked adhesiveness.  The general transverse direction of the fibers inclines from the radius of the cochlea toward the apex.

Who Was Irving Hardesty?

There is not much information available on this cochlear explorer, but Schacht and Hawkins (2004) report that  Irving Hardesty was born in Beaufort, NC in 1866.   He matriculated at the University of Chicago, where he received a Ph.D. in 1899, probably in anatomy.  Hardesty next surfaces in 1901 at the University of California, San Francisco where he wrote his famous paper on the study of the tectorial membrane. Entitled  “On the nature of the tectorial membrane and its probable role in the anatomy of hearing, it was published in the American Journal of Anatomy in 1908.  This is the article that led to the structure being named after him.

The best description of Hardesty’s work comes from Schacht and Hawkins, who say that he was frustrated with the shrinkage characteristics of the specimen preparations of the time and so attempted to fabricate frozen sections.  While the frozen sections were unsuccessful, he began using “Zenker’s fluid” to prepare specimens and found this helpful in his study of the tectorial membrane. While we remember Hardesty for the membrane that bears his name, we may forget the theoretical concepts that he derived from his studies:

 ‘The theories in which the basilar membrane is considered the vibrating mechanism in the cochlea are considered untenable, and an application of the telephone theory to the tectorial membrane as the vibrating mechanism is suggested on the basis of its logical position, its extent, shape, proportions, consistency and structure, and the probable character of the transformed and transferred sound waves in the endolymph of the cochlea.’

Later in his career Hardesty joined the faculty at Tulane University and became President of the New Orleans Academy of Science. He died in New Orleans in 1944.  There are no pictures to be found of Irving Hardesty, simply the family burial plot in Metarie, LA.