56 lioyal Society. 



The anatomy and attachments of the stapes are next minutely 

 described. The base of this bone, generally stated by writers on 

 the physiology of the ear as being attached to the margin of the 

 fenestra ovalis by a simple membrane, ligamentuni annulare haseos 

 stapidis, is shown to possess some points of considerable interest. 

 Instead of a simple margin to which the ligament above noticed is 

 fixed, the base of the stapes is stated to present a circumferential 

 surface for articulation with the fenestra ovalis. This circumferen- 

 tial surface, larger at the anterior and posterior extremities than in 

 the middle, is covered by articular cartilage. The surface of the 

 fenestra ovalis, to which the circumference of the base of the staj)es 

 is applied, is somewhat larger than that of the stapes. It is smooth, 

 has a very compact structure, and is not covered by cartilage. 



The base of the stapes is attached to t\\e fenestra ovalis by two 

 ligaments. The inner or vestibular ligament passes from the inner 

 margin of Xhe fenestra ovalis to the inner margin of the circumferen- 

 tial surface of the base of the stapes. The outer one passes from 

 the outer margin of the. fenestra ovalis to the corresponding margin 

 of the stapes. These two circular ligaments leave between them a 

 space which may be considered as an articular cavity ; this cavity 

 always containing a sufficient quantity of fluid to lubricate the arti- 

 cular surfaces of the bones. 



The movements of the stapes are of two kinds, one being produced 

 by the action of the tensor tympani, the other by the stapedius 

 muscle. If the tensor tympani muscle be drawn in the direction of 

 its course, while the cavity of the vestibule has been exposed to 

 view, the base of the stapes will be observed to be slightly projected 

 towards the cavity of the vestibule, and it returns to its normal posi- 

 tion as soon as the muscle is left quiescent : the ligaments above 

 described appear to be the organs whereby the stapes is again 

 drawn outwards. In this movement the stapes may therefore be 

 described as passing to and fro within the fenestra ovalis, as a 

 piston does in a cylinder. The second movement of which the base 

 of the stapes partakes is one of rotation, and it is effected by the 

 stapedius muscle. To show this movement, it is requisite to per- 

 form one or two careful experiments. The stapedius muscle being 

 exposed in its canal, while the stapes is left undisturbed in the tym- 

 panic cavity which has been laid open, if the muscle be drawn in 

 the direction of its course, the anterior crus of the stapes is observed 

 to move slightly outwards and backwards. In what manner the 

 base of the stapes is affected during this movement of the crura it is 

 difficult to decide, but it would appear probable that its anterior 

 part is drawn outwards from the cavity of the vestibule while the 

 posterior part is pressed inwards, though to a less extent. That 

 the action of the stapedius muscle is to relax the fluid of the laby- 

 rinth, is however shown by the following experiment. The tym- 

 panic cavity and stapedius muscle being exposed to view, a section 

 is to be made through the cochlea, a small portion of the scala ves- 

 tibuli being left continuous with the cavity of the vestibule. If the 

 stapedius muscle be now drawn in the direction of its course, the 

 fluid in the cut extremity of the scala vestibuli is observed to recede 



