FORMATION OF THE EAR-LABYEINTII. 



771 



the vesicle exhibits is by the extension of a process upwards and 

 backwards, which remains permanent in the lower vertebrata, but in 

 mammals is obliterated, its vestifi^es remaining in the aqueduct of the 

 vestibule. The semicircular canals next appear as elongated elevations 

 of the surface of the primary vesicle : tlie middle portion of each ele- 

 vation becomes separated from the rest of the vesicle by bending in of 



Fig. 574. 



Fig. 574. — Views of the 

 Cartilage of Meckel 

 and parts connected 

 WITH THE First and 

 Second Branchial 

 Plates. 



A (after Kolliker), bead 

 of a fcetus of about eigh- 

 teen weeks, showing the 

 cartilage of Meckel in con- 

 nection with the malleus 

 and the surrounding parts. 



M, placed upon the 

 lower jaw indicates the 

 cartilage of IMeckel of the 

 right side. 



B (from nature). An 

 enlarged sketch explana- 

 tory of the above view ; z, 

 the zygomatic arch ; ma, 

 the mastoid process ; ml, 

 jDortions of the lower jaw 

 of which the parts near 

 the angle and the sym- 

 physis have been removed ; 

 M, the cartilage of Meckel 

 of the right side ; M', a 

 .sratdl part of that of the 

 left side, joining the left 

 cartilage at s, the symphy- 

 sis ; T, the tympanic ring ; 

 m, the malleus ; i, the in- 

 cus ; s, the stapes ; sta, the 

 stapedius muscle ; st, the 

 styloid process ;p,A,<7, the 

 stylo- j)haryngeus, stjdo- 

 hyoid, and stylo-glossus 

 muscles ; stl, stylo-hyoid 

 ligament attached to the 

 lesser cornu of the hyoid 

 bone ; hij, the hyoid bone ; 

 th, thyroid cartilage. 



its walls under it, and thus the elevation is converted into a tube open at 

 each end, vyhich subsequently becomes elongated and acquires an ampullar 

 dilatation. The cartilage wliich forms the osseous labyrinth is con- 

 tinuous with that of the rest of the primordial cranium. The car- 

 tilaginous walls of the cavity are united by connective tissue to the 

 vesicle ; this connective tissue, according to Kolliker, becomes divided 

 into three layers, of which the outer forms the lining periosteum, the 



3 D 2 



