ATTACHMENT OF THE STAPES TO THE FEXESTRA OVALIS. 127 



that there are a large number of intercommunicating cavities, 

 whilst in the amphiarthroses generally there is only a single 

 irregularly shaped cavity. 



If we altogether disregard mere nomenclature, it appears from 

 our description that the base of the stapes is attached to, or 

 inserted into, the fenestra ovalis in quite a peculiar manner, a 

 fact which indeed Hel.mholtz has established experimentally. 

 This observer has demonstrated that the mobility of the base of 

 the stapes is very small, the greatest excursion it can make not 

 exceeding 1-lSth to l-24th of a millimeter. According to the ear- 

 lier accounts of the mode of attachment of the base of the stapes 

 with the fenestra ovalis, a considerable degree of mobility 

 occurs between them. All the diameters of the osseous fenestra 

 ovalis are, however, so far diminished by the elastic cushion of 

 the hyaline cartilage that the base of the stapes, which is also 

 covered with cartilage, is received into it, and but little room 

 for movement consequently remains. I have still to call atten- 

 tion to a structure on the tympanic surface of the base of the 

 stapes, which, from the observations I have hitherto made, I 

 must regard as a muscle of vegetative life the musculus fixator 

 baseos stapedis. 



At about the distance of a millimeter from the fenestra 

 ovalis, a narrow crest of bone, with a transverse diameter of 

 about O'OSO of a millimeter, springs from the posterior and 

 inferior border of the base of the stapes, and projects into the 

 tympanic cavity. In surface views this appears in the form of 

 a low sinuous elevation which terminates with a blunt point 

 that is opposite the projecting border of the base of the stapes. 

 Its importance is only recognizable in transverse sections. 

 The mucous membrane presents the same relation to this crest 

 of bone as to the others that project into the tympanic cavity. 



Forming a direct continuation of this ridge is a yellowish 

 dense tissue, which is attached to the angle between the crus 

 of the base of the stapes and the somewhat everted part of the 

 base. This tissue is connected and continuous, however, not 

 only with the bone, but also with the cartilaginous invest- 

 ment (fig. 317). 



In macerated transverse sections which have been subjected 

 to imbibition, long coloured stride are visible, which, in isolated 



