202 Mr. Carlisle on the Physiology of the Stapes. 
then it is the left stapes. The arch above the straight side of 
the basis is more rounded than that above the curved side ; the 
latter being an intersection of two curves like the Gothic arch. 
I have never seen that expansion of membrane across this 
arch, described by Du Verney ; and, from the great number 
of ears which I have attentively examined, am induced to think 
that a pellicle of mucilaginous fluid, which often covers the 
recent bone, has been mistaken for a membrane. 
The stapes stands perpendicular to the plane of the mem- 
brana tympani ; a plane drawn through the crura, parallel to 
the length of the basis, equally bisects the cavity of the 
tympanum. 
The stapedeus muscle arises within a special cavity in the 
petrous portion of the temporal bone ; it is a short, thick mass 
of red fibres, covered by fascia ; and sends forth a round 
tendon through a small osseous aperture at the point of the 
pyramidal eminence, which unites to the colluin stapedis in an 
angle of 50 degrees, toward a line drawn perpendicular to the 
plane of the basis, and obliquely across its convex side, in an 
angle of 5 degrees from the bearing of its straight side. The 
action of the stapedeus muscle is to draw the capitulum down- 
ward, and toward the curved side of the basis. This oblique 
motion depresses the end of the basis under the curved crus, 
whilst it rotates the incus upon its short leg, and presses its 
articulation with the malleus into closer contact : but the stapes 
is not withdrawal from under the long leg of the incus, being 
prevented by the strong connecting ligaments. 
The smaller angle of the tendon crossing the parallel of the 
crura over the convex side of the basis, necessarily depresses 
that edge, the straight side acting as a hinge. The extemus 
