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Show 144 ON 'fHIJ; STHUOTUHJ!; O.b' TIIJD r ULL. f . t others which app ar, not in cartilag ' but in the lll 'lll-lOill WO l l' , f' } '} br.a nou 1· oof of the skull abov t 1e 1m1t . . .t 1 cnrt1 ag , and so g1· ve n· e to tl1(a. t p. art. of the quama ocCiplil mar1c d SO'.. , The basi-sphenoid 1s d v loped from tw centr of os l.fiea-tion which appear in the floor of the sella ~u1·ci~a, b~1t sp edily coalesce into on . Two eparate c ntr of 1ficatwn appear in the cartilage bet we n th s and tho ali 'ph noid , '1lld form the Zingulr£ sphenoiclales. Ea h alisphenoid i ' dev lo1 d from a .FiO". 59. Fig. 59.-A, upper, aud B, under view ot' the basi · cranii nnd periotic .cart.ilage .o~· '\ human fcetus eight inches long. The alisph noiual and immediately a<.lJncent p:u t:; ol the basi-sphenoid are omitted. The cartilage is darkly shad tl, while the o,seot:s .de· posits are left white, or but lightly &haded. The greater part of the supra-occlpl~a~ is cut away. The clear spac s close to the dottctllines J n<.liug li·om t.ty are npc~·tutt>~ in the rartilage. The cpiotie dassifi ·alion ha · not yel ~1ppcmcd, nnd the pro-otiC and opisthotic ossifications are quite di~;tiHct on th 1 ight side. THE DEVELOPMENT OF 'l'IIE HUMAN SKUJJTJ. 146 single centre in its cartilaginous predecessor, but the parietals are the result, not of the ossification of cartilage, but of that of the 1nembrane which roofs in the skull. Each has its own centre of ossification in this membrane. The presphenoid arises by two separate centres of o ification, one on the inner sid8 of each optic foramen. (Fig. 59, P.S.) These centres coalesce with the orbito-sphenoids of their own side before they unite with one another.* The o ·seous orbito- *The mode of ossification of the sphenoid bone is one of the mo t difficult questions in o teogcnesis. Mock l has worked out the problem at great length in his "Archiv," Bd. i., and thus sums up his results in the "Ilandbuch der Men chlichen Anatomic," Bel. ii., pp. 102-4 :- " In the third month, the :first osseous nuclei appear in the two great wings, and soon afterwards tho int mal pterygoid processes begin to ossify as separate bones. Next, a third pair of ossifications appears in the external circumference of the alre minores; and then, about the fourth month, a seventh and eighth nucleu , which lie side by side in the body of the sphenoid. In the fifth month is formed, alongside this fourth pair, a fifth, between it and the great wings. Upon thi the two median nuclei of the body coalesce. Soon ari cs a sixth nucleus, on the inner ide of tho optic foramen, and then a seventh appears between this and the fourth, o that, about the beginning of the seventh month, the sphenoid consists of thirteen s parate bony nuclei, since, notwithstanding sev n pairs have arisen, the two primary nuclei of the body early coalesced into one. "From this time forth the number of the nuclei diminishes still m01·e considerably by coalescence. Those nuclei coalesce earliest which give rise to the portions of the sphenoid, which persist in a separate state longest. The fourth, fifth, and seventh pair soon unite into one piece ; the first and second, coalescing on each side, constitute two other pieces; tho thii·d and sixth two others; whereby, in tho eighth month, the sphenoid consists of five pieces-the two greater wings, the lesser wings, and the body. Somewhat later the two lesser wings coalesce into one, and the sphenoid now consists of four pieces ; thei·eupon the body and the anterior pieces uuito, so that in the fully-formed footus the sphenoid consists of three pieces, the greater wings and internal pterygoid processes being still distinct; but in the fir t month after birth these three pieces unite into one.'' 'fhe fifth pair of ossifications here mentioned arc the lill[jul;;e; the sixth, those which give rise to the presphenoid. Meckel's seventh pail· of ossification , which arise between the fourth (basi-sphenoidal) and the sixth (presphcnoidal), and are said, in the "Archiv, ., to coalesce :first wi1h one another, and then with the basisphenoid, appear not to have been observed by other anatomists. I have not seen them, and they are not mentioned by Virchow, the latest writer on the subject. ,... .:Vircho~ w1:ites (." Entwickclung des Schadel-grundes," 1857) :-"The posterior sp~en01d ar1ses (1f we leave out of consideration the internal pterygoid proces es whwh are developed as separate and independent bones), according to most authors, from three nuclei, but, according to my observations, from six. Two of these belong to the alre magnre (alre temporales), or lateral arches (Bogenstiicken) of the parietal vert~bra. They arise in the third month, and the external pterygoids are produced by dn·ect outgrowths from them. In the third month, I also :find two oth<'r rrntres L |