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Show 146 ON THE STRUCTURE OF TIIE S K UL T-.~o I 'd sp 1eno1 s a1:1 s e each bJ'r one centr in the corre po•n ding carti•l ages. The. frontals, on the other hand, arc develop d,, hke the pnnotalR, eac 11 f rom on e Centre iu thP' n1 mbranous rooi of. th skull. Thus we arrive at the singular re ult that, wlnle all the Lones of the basi-cranial axis, and all the lateral bon s of the throe of ossification which brlong to th of th lingnhe, nnd ar 'C']Xl.n.tt d by dis-t .m e t 1a y CI'S of c·a rtilaoo- from th th. crs. . 'l' h. o ·iii ·ation of .t h o lingula .i s nlm.o RL compl et e I·n tho fourth month • an. d It 1z 1. • ou t. of .a ll r latwn to the. dnncns10ns of the other parts. It is a th1ck , obtu ' ly- ylindncnl proc ss, winch coa]c. ccs primarily with tho body, and bas ~o thin g to d with tho nl; . Tho l~ngula is _t)H'rcfore similar to an ant rior or iu£ nor trnn vor e pro ~ (Pamp physts, Owcll); nnd the sulctts caToticu , notwithstanding it po. ·iLion in th inner ide of tho lingnla, r , embles an open j omrnen veTtebrale. Ilow vcr, Arnol<l's opinion that tho Vi<lian canal answers to th canal for the vertebral artery, notwith ·tanding it is placed on tho inner side of the lingula, des rves th car ful ntt ution of comparative allatomists. The o sification of th body begin in th third month, cxn.ct.ly under tho pituitary fo a, which is already pr form d in cnr t.ila~e. r .erckring wa tho fir -t. to point out that h ere the adjacent. o~ cous centr at fir t nn , and ~h~t th~y umt., and form a biscuit- haped rna s m th fifth mouth. One h .. mv tlm; ·c1mhmuln even in the middle of the third month. K ulli.k r and I mys lf have mot with it in fretu es of throe months. Otl.l r ob rv r ', a' N .. bitt n1H.l l\1:ny r, spcnk of a singlo centre in the third month, and in the fourth of two c ntr , wllich must bo regarded as the result of the erron on combinat ion of <lifl''r 'nt. intlivitlual cas H. I find constantly, in the brginnin !Y of t ll third month, two nucl i, which arise ncar the upper surface in the anterior wall of t.h pituitary fossn, mul arc !icparatcd by n broad layer of cartilag . V cry oon, howe •r, only a ·ingl o. ·.· ous rna s is present in the interior of tho body, which ext nd t hrou o-h the whole thiclrncsl::! of tl1o cartilage, while anteriorly aml post riorly it i t ill nvclop tl in cnrt.ilagc. In a frotus 19 centimctr s [7! inches] lon g, I aw th implo o scous nucleus in tho bottom of the sella, as a trausver e plat which l1ad not yet unit. d with the lingula." "The anterior sphenoid i d v 'lop d by iho gmdual ale. c nee of four o::;scous centres, of which again two belong to the body un<l on to ea ·h of tho lcssl'r wings. The latter are developed earli r than th form r. Th y connnenco early in the third month, in the anterior clinoid p ro • e ', which nrc q nit thiek .nncl osseous at a time when everything else in th • ani rior spbFnoid is hyaline curtilage, n.nd therefore arc quite ·imilar to the lingulc. '. F rom thi p int os~ifieation progresses rapidly, at last creeping rounu the eir •umfer 'nrc o(' th optie foramen to tlJO body of tho ala and to its anterior root. About tho 1ift.h mouth the l ·s or wing is completely solill in all part . On th oth ' 1' l1rtml, tho nuclei in th • body mostly appear somewhat later, usually in th • fourth month, and at th iun r edge of the optic fornmcn, so that they arc at fir ·t pamtcd by a tolerably broad m dian lam lla of c~rti lagc, which is continued into tho ethmoid cartilage and eJJtum nm·iurn. A nmon .now very soon tak s plac b otw nth ' ntr . of the body nnd thos in tho lcs.sor wmg~, so tllat tl1e optic foramen is smTouuu 'U hy bon . . . . . Ln,tcr, nt t tmcs, as It appears, as early as the fifth montb, th • t~o lat ml masses unite into ulargc~· ccn.tr~l piece, which is free , uperiorly, while b low and anteriorly, in tho middle lmc, It 18 surrounded by broad mass s of cn.rtilag ."-Vireh ow, lor. cit ., pp. 15-18. THE DEVELOPMEN'£ OF THJ~ HUMAN SKULL. 147 cranial arches, are primarily developed in cartilage, only one of the superior elmnents of these arches-the supra-occipital (SO) -is so; while tho upper or "interparietal" portion of the squama occipitis ( 8 01 ) and the two other pairs of superior elen1ents of the arches are developed altogether fi·om membrane. Fig. 60. Fig. GO. -- Longitmliual and vert ical section of the busi;:; crunii of a fretus somewhat older than the toregoing (Fig. 59). The basi-sphenoidal and p resphenoidal centres h:w e coalesced; but they and the basi-occipital are severalJy separated by wiclc inter ·ticC's of cartilage, of \vhioh the whole ethmoidal region is still cou:;tituted. The ethmoid is developed from a single centre, arising in the internasal cartilage. Its so-called lateral masses, with th two upper spongy bones, are likewise developed each from a single centre within the superior part of the inflected lateral cartilages whieh wall in the olfactory sacs. The inferior turbinals are ossifications of the lower parts of these cartilages. But the nasal bones are developed within the perichondrium, which is continuous with the membrane in which the frontal bones are developed, and the vomE.~r is produced within the pericho~drium on the under-surface of the internasal septum. The bones of Bertin are also said to be developed fron1 membrane- the perichondrium of the presphenoidal cartilage, or the walls of the olfactory sacs. The development of the temporal Lone is pa.rticulal'ly worthy of attentive consideration. The squamosal and the tympanic elements are developed in membrane, and, at first, lie perfectly loose in this membrane, upon the outer sid of the periotic cartilage. The tympanic is a delicate nng, open above; th squamosal is a mere rod, the zygoma, with an expanded posterior L2 |