168 



FORMATION OF THE AUDITORY OSSICLES. 



The most obvious interpretation of these appearances would seem to be that both the 

 malleus and incus are developed from the cartilaginous bar of the first or mandibular arch. 

 This view is not, however, universally held. For, as the several illustrations show, the second 

 or hyoid bar is also connected to the developing incus, through which it is joined to the periotic 

 capsule. Hence it has been inferred by some that the incus balongs to the hyoid bar, and not 

 to the mandibular (A. Fraser). Others have looked upon it as representing a hyomandibular 

 cartilage, like that which in Sauropsida forms a common suspensory apparatus for both 

 mandibular and hyoidean apparatus (Huxley). This hyomandibula itself, however, may repre- 



Fig. 200. CONDITION OF MECKEL'S CAR- 

 TILAGE AND THE HYOID BAR IX THE 

 HUMAN FCETUS OF ABOUT 18 WEEKS, 



(Kblliker.) 



B, is an enlarged sketch by Allen 

 Thomson, showing the relationship of 

 the several parts better than in A. 



z, zygomatic arch ; ma, mastoid pro- 

 cess ; mi, portions of the lower jaw left 

 in situ, the rest having been cut away ; 

 J/, deckel's cartilage of the right side, 

 continued at s, the symphysis, into that 

 of the left side J/', of which only a small 

 part is shown ; T, tympanic ring ; m t 

 malleus ; i, incus ; s, stapes ; sta, stape- 

 dius ; st, styloid process ; p, h, //, stylo- 

 pharyngeus, stylohyoid, and styloglossus 

 muscles ; stl, stylohyoid ligament attached 

 to the lesser cornu of the hyoid bone, ky ; 

 th, thyroid cartilage. 



sent an upward prolongation of 

 Meckel's cartilage, and would then 

 belong to the 1st visceral arch 

 (Peters). Lastly, yet another solu- 

 tion of the question has been offered, 

 viz., that both incus and malleus are 

 hyomandibular (Albrecht, G-adow). 



The last mentioned opinion is based 

 mainly upon considerations of com- 

 parative anatomy, which can hardly 

 be left out of account in dealing with 

 the morphology of these structures. 

 In lower Vertebrata the suspensory 

 apparatus of the lower jaw comprises 

 besides the hyomandibula. common 

 to it and to the hyoid apparatus, a 

 large bone, known as the quadrate, 

 by means of which, either directly or 

 with the intercalation of an os arti- 

 culare, the lower jaw is united with 

 the basis cranii and periotic capsule. 

 Reichert looked upon the incus as the 

 nomologue of the quadrate, and the malleus as that of the os articulare ; and the same view 

 was taken by Gegenbaur. Huxley, on the other hand, came to the conclusion that the 

 homologue of the quadrate bone of reptiles and birds is to be found in the malleus, and that 

 the incus represents a portion of the hyomandibular bar, which, as above stated, is common to 

 Oth first and second arches. Various other observers have concluded that the quadrate of 

 lower vertebrates is represented in mammals by the zygomatic process of the squamosal. 

 Gadow, however, looks upon it as represented by the tympanic ring of mammals. 



stapes has been variously described as representing: 1, a part of the hyoid arch 



ichert) ; 2, a part of the periotic capsule which has become detached (Parker) ; 3, in part 



or wholly, the hyomandibula of lower vertebrates (Gegenbaur, Huxley, Albrecht, Gadow); 



4, hyomandibula and detached periotic cartilage conjoined (Gradenigo) ; 5, as an independent 



circular deposit of cartilage around the stapedial artery ' (Salensky, Fraser). It is at any rate 



sely connected with the hyoid bar., which forms from above down the tympano-hyal and 



1 This artery disappears in man, but is persistent in many mammals. 



