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Show 160 ON THE S'l'RUC'l'UHE OF THE SKUJ,L. The axis of the second visceral arch becomes converted above into the stapes, below into the styloid cartilage, the stylohyoid ligament, and the lesser cornua of the hyoid bone, the body and greater cornua of which are developed from the third visceral arch. Between the styloid cartilage and Fig. 64. Fig. 64.-Part of the skull of a human fretus nt about the sixth month, dissected to show the auditory o sicles and Meekel's r.artilage, Jl[cfl. Gl, the glenoid cavity. The mnrgo tympanic11s and adjacent part of the squamosal arc repre en ted as if they were transparent, in order to show the po ·i tion of the mallc.u (m) and incus (i). The tympanic bone ( Ty) is merelJ indica tell. Co., the ochlca. the stapes it is n1odified o as to fonn the stap dins muscle. A centre of ossification app ars in th styloid cartilage, and, extending upwards and downwards, gives ri e to the pyramid and the styloid proce . Some authors, however, give a omewhat different aecount of the metamorpl1oses of the cartilaginou axes of the first and second visceral arche to that which I have detailed, and which is based chiefly upon th r searches of 1\:Ieckel, Rathke, and Reichert. Thus Gunther,* while he agrees with Reichert that the cartilaginous axis of the first visceral arch divides into three portions, the uppermost of which (that which is primitively connected with the skull) early disappears, while the middle and lower becom converted respectively into the incus and the malleus with Meckel's cartilage, differs from * Beobachtungen tiber die Entwickelung des Gehi)rorgans bei Menschen uncl hoheren Saugethi ren. 1842. THE DEVELOPMENT OF THE HUMAN SKULL. 161 h ii~ regarding the. origin of the sta es A . . . . wnter ·-" Th 'lcll a· . . P · ccm dmg to this . . e mic e I VISIOn of the cartila()'inous axis 1' ~tself to the vesicular cartilaginous labyrinth :nd l 't app Ies Into contact with tho labyrinth it s d ' t w len I comes which is received b T • . ' en s 011 a small nodule, nod l . ) a plt, the future fenestra oval is." The ~ e grows out Into a process, the lower part of which b ~~~~~gi!~n:h~n tthe upphe~·l, afnd eventually articulated, is co:~ s apes, w 1 e rom the upp . ·t .· . long process of the incus. 8l pal onginates the The. auditory ossicles are at first altoo·ether . tympal:IC cavity; and as the latter enlargeso its outside the br·1ne Is f1 t d ' mucous mem- < re ec e around the ossicles. Th d . f matter for each ossicle commences in tile e ~phosit...:~~· osseous tl t h ' penc onunum and o:::b:~:~re~ three ossific centres, independently of that f;r the .It can har~ly be doubted that there is much et leainecl respecting the first steps in the d I y to be ossicula auditu.s. but th . . . . eve opment of the dif.ficulties. * ) e InvestigatiOn Is one fraught with tom* e Sxeev.m~f. agitot ot Robin, "Cartilage de Meckel· " Ann. des Be. Nat. Se. IVe. |