OCR Text |
Show 1869.] THE MALLEUS AND THE INCUS OF THE MAMMALIA. 399 outer wall of the periotic capsule, just behind the articulation of the quadrate bone. A. The auditory region, the tympanic membrane being taken away, in a Fowl. Qu. Quadratum. S.St. Platner's ligament. E.St. The extrastapedial cartilage, the edge of which is fixed to the tympanic membrane, b. The end of the extrastapedial which is fixed to the posterior boundary of the tympanum, c. The ascending process. I.St. The infrastapedial process. B. The outer end of the stapes separated from the stem where the latter begins to be ossified. Turned round and magnified. I see no room for any doubt that this ascending process and the elastic ligament represent the suprastapedial cartilage of the Crocodile. As in the Crocodile, the posterior end of the extrastapedial cartilage is closely connected by fibrous tissue with the posterior boundary of the tympanum and the tympanic membrane ; but I have been unable to discover even a rudiment of a styloid cartilage. The inferior, free, curved process of the stem of the stapes, which may be termed infrastapedial (I.St) seems at first to answer to that cartilage; but its relations are quite different. Thus the Lizard, the Crocodile, and the Bird present a complete series of modifications of the parts described. In Sphenodon the hyoidean arch is histologically continuous throughout its entire length; and in its upper part is a rod of cartilage which, at one point, passes into the stapes. In the Crocodile, the upper part of the hyoidean cornu has no direct connexion with the lower, and the rudimentary styloid part is not histologically continuous with the stapedial part. In the Bird the styloid part has vanished, and the suprastapedial is represented only by fibrous tissue. |