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Show IH2 ON THE VJ~R'l'EBI~A'rE SKULL. ing into any details which w?ro not strictly ncce . ·ary; but thoro remains one part of the cranium-the tmnpora1 b~n -t~1e trn~tnre of which 1nust be carefully and thoroughly 1nv t1gatcd, 1C we desire to understand the Inodification undergone by the bones which correspond with its c n tituent l n1 nt in other Vertebrata. Viewed from without, the ten1poral bone pro nts the well-known pars squamosa (Sq.) and pa1~s 1nastoidea (M), in the re-entering angle between which, th tyn1panic el 1nent ('Ty.) is fixed (Fig. 55). No suture separates the pars squam.osa frmn the pars mas-toidea, but tho posterior limits of the form er are indi a ted, in tho first place, by the curved ascending portion of tho po torim· root of the zygoma (a b), which bounds the attachment of the tmnporal muscle; and secondly, by a curved ridg , convex backwards and differently defined in different subject -tho 1nargo tynlpanicus of Henle-which pa es downward , b hind th auditory meatus, until it cuts the contour of th tympanic bone. Ncar the upper end of this ridge, or "post-auditory proc' s," is an elongated "post-auditory fo . a" (b), more n1ark d in old than in young subjects. The portion of tbe squamo al el ment, th free dgo of which terminates in this ridge, forms an arch, of whi ·h tho posterior pillar constitnt s the posterior and upper wall of the auditory meatus, while the anterior pillar fonns the front boundary of the glenoid cavity. The centre of tho arch is iuterrupted by the middle root of the zygoma (e), or " the po t-glonoidal process " of the squamosal, which runs, as a wedge-shaped ridge, transver ely to the span of the arch . . The upper edge of the anterior wall of the gutter-shaped tympanic bone (which forms the hinder boundary of the glenoid cavity), unites with this ridge, crossing its direction obliquely inwards and forwards. Beyond the ridge it is no longer united with the squamosal, but, keeping its oblique direction, crosses rather to the inner side of the lower edge of that bono, and leaves the Glaserian fissure between the squamosal and itself. A section taken through both the external and the internal anditory meatuses (Fig. 5o) shows that this arched plate of the 'l'IIE S'rRUC'fORE 011' 'l'IlE HUMAN Sl\UI,L. 103 . qmunosal is interposed between the upper 11alf of the tympanic aud the upper part of the pars petrosa and pars mastoidea, the depth of the 1nterposed squamosal bcino· oTeatest posto · ·] wh I'1 e 1't d.I m1.n 1.s I1 es to nothing anteriorly. 5 b flOl y, . . The upper re?ion ?f the pars petroaa, however, does not due~tly ab?t, by 1ts tlnck 1nass, ngain t the squamo al, but by a tlun hor1zontal plate, wbich roofs over the t . 1 · .Y mpannm, t 10 Fig. 56. A -- ... ~ _, Ofi .• O. B Fi r:G v· g. u .- Iews of the petrous and 1 m · · . skull1·epresented in Figs 48 rl J9 panic ,r_ortJOns 0 ~ the r1ght temporal bone of the the bone; B, its posterior ]~~~f. j ;ag~utied two dwmeters.-A, the auterior half of proces~us cochJeariformis. b c l' ·b ., .mter~al meatus; E.M, external meatus. a lie ; c, groove for the ty'm ' c.1am erbm WhiCh the heads of the malleus and i~cu~ c,a n al ,· a' c e'"ternal " . . pamI c mem rane '· S , V..O ., s npel .·J Ot . veJ ·t·I ca1 semi.C.U Clllat· ' '' " < "emlCll'CU ar ca ]• · · r Go, cochlea; P, Pyramid . F. 0 f ' na ' p.c. '. post!'l'JOJ' vertical semicircular canal ; for portio mollis. ' · ., enestra ovahs; Vlf, canal for portia dura; VJJl, |
