260 



AUDITORY OSSICLES 



converted into bone the cartilage of Meckel disappears, but meantime on its proximal 

 end a small membranous ossicle appears, which joins the malleus as its anterior 

 process. 



The tympanic ring is also a membrane bone. It appears in the third month 

 below and lateral to Meckel's cartilage, and is secondarily attached at a later date 

 to the petrous and squamous. When this union is effected the ossicles originally 

 on the outer side of the ear-capsules are included in the tympanic cavity. 



Among other recent writers who have worked at this old problem, J. F. Gemmill ' agrees 

 with Broman in respect of the stapes, but Fuchs, 2 working on rabbit-material, has come to con- 

 clusions shared also by Driiner, 3 which revert to those of Parker in his earlier papers (1877), and 



m a, 



FIG. 314. CONDITION OF MECKEL'S CABTILAGE AND THE HYOID BAB IN THE HUMAN FCETUS 



OF ABOUT EIGHTEEN WEEKS. (Kolliker.) 



B is an enlarged sketch by Allen Thomson, showing the relationship of the several parts 



better than in A. 



z, zygomatic arch ; ma, mastoid process ; mi, portions of the lower jaw left in situ, the rest 

 having been cut away ; M, Meckel's cartilage of the right side, continued at s, the symphysis, into 

 that of the left side M', of which only a small part is shown ; T, tympanic ring ; m, malleus ; i, incus ; 

 s, stapes ; sta, stapedius ; st, styloid process ; p, h, g, stylopharyngeus, stylohyoid, and styloglossus 

 muscles ; stl, stylohyoid ligament attached to the lesser cornu of the hyoid bone, hy ; th, thyroid 

 cartilage. 



of Gruber (1877) viz. that the stapes blastema is primarily connected with the auditory capsule 

 and is only secondarily connected with the hyoid arch. Fuchs and Driiner also believe that the 

 connection of the malleus and incus with Meckel's cartilage is a secondary one. 



The ontogenetic history of the auditory ossicles, as described by Broman, affords additional 

 evidence that the incus is a separate element, and confirms the view that it represents the 

 quadrate bone of lower forms ; while the malleus is the upper end of the primitive mandible, 

 and when ossified is the homologue of the os articulare (Gaup). 



1 Brit. Assoc. Report, 1901. 2 ArchivJ. Anat. Suppl. 1905. 5 Anat. Anzeiger xxiv. 1904. 



