Mr. Carlisle on the Physiology of the Stapes . ?oi 
The collum, which unites the capitulum to the two crura. 
And 
The basis, on which the expanded crura rest and terminate. 
The capitulum stapedis has a shallow, concave surface, to 
receive the os lenticulare, or epiphysis connected to the long 
leg of the incus. ( Vide Plate IV. letter c. ) Around this joint 
a strong membrane is applied in the manner of a capsular 
ligament. The capitulum is seldom placed exactly on the top 
of the Gothic arch formed by the crura, and the crus imme- 
diately under the stapedeus muscle, is always the thickest, and 
most curved. ( Vide letter a.) 
The collum is hollow, being only a thin shell of bone ; on 
its side is a small tubercle, to which the tendon of the stape- 
deus muscle is affixed. See letters a and h. 
The crura are curved, and their interior surfaces are grooved, 
leaving only a thin osseus plate. 
The basis is exactly adapted to the the fenestra ovalis, 
more properly called fenestra vestibuli by modern anato- 
mists, and the two ends project beyond the crura. The upper 
surface is generally concave, the under surface slightly convex ; 
and here a rising border marks the insertion of the membrane 
which connects it to the edges of the fenestra vestibuli. Vide 
letter c. The outline of the basis somewhat resembles a long 
semi-ellipsis, one side being nearly straight, and the other 
convex. This figure appears adapted to the expansion of the 
basis, without increasing the bulk of the bone, whilst it gives 
leverage to the muscle. 
When the stapes rests on its basis, with the straight side 
next to the observer, if the more curved leg be toward the 
left, then it is the stapes of the right ear ; but if on the right, 
MDCCCV. D d 
