ATTACHMENT OF THE STAPES TO THE FENESTRA OVALIS. 125 



The cartilage at the last-named part is invested by nucleated 

 fibrous tissue, constituting the perichondrium, which is con- 

 tinuous with the lining membrane of the vestibule. The 

 homogeneous matrix of the cartilage is distinguished from the 

 adjoining osseous tissue by its yellowish tint, and in tinted 

 specimens the rounded cartilage cells are brought clearly into 

 view in consequence of the intense colour of their nuclei, as 

 compared with the colourless matrix. 



The cartilage cells undergo a change in form near the 

 centre of the vestibular surface of the base of the stapes, be- 

 coming elongated, with their longest diameter running from 

 before backwards. 



The margin of the fenestra ovalis also possesses a cartilagi- 

 nous investment. The thickness of this at the posterior border 

 is equal to that covering the opposite surface of the base of the 

 stapes : anteriorly it measures from 0'040 to 0*048 of a milli- 

 meter. The cartilage terminates more abruptly towards the 

 tympanic cavity than in the vestibule, where it reaches beyond 

 the margin of the fenestra ovalis, and becoming thinner extends 

 for some distance upon the surface of the vestibule. 



A layer essentially composed of elastic tissue, and equal in 

 thickness to the hyaline cartilage, is continuous with this both 

 at the fenestra ovalis and at the border of the base of the 

 stapes ; the layer is of very close texture, and it becomes very 

 conspicuous in macerated specimens, in consequence of strongly 

 imbibing the colouring material. The fibres run from one car- 

 tilage towards the other, and at the point where the opposite 

 sets meet a system of lacunae is formed by their plexiform 

 inter communication, which is filled with fluid. Towards both 

 the vestibule and the tympanic cavity this dense elastic tissue 

 extends from the one cartilage to the other, forming a ligamen- 

 tum orbiculare baseos stapedis vestibulare, and in the tympanic 

 cavity a weaker ligamentum orbiculare baseos stapedis tym- 

 panicum. The latter is continuous with the mucous membrane 

 of the tympanic cavity, without however being so sharply 

 defined at its circumference, as is shown in fig. 318. 



At the upper and lower borders of the base of the stapes 

 the nature of the connection chaiges in consequence of the 

 uniformly thick circumference of the base being bevelled off 



