| OCR Text |
Show VER'fEBTIATE SI<Ul,L. 290 ON THE STRUCT 0 l·:•> E OF THE ~ • . f a di.n o· throng1 empty speculations upon become weary o w ::, " 1, , irrelative repeti.t iO. n " an d " connatw. n " and "coa.l escenceh,. d . t l A who are calle 1n o so ve . . " the De~ ex mac ~na . . h "transpo·msi tion, ·t'l does one sympathise Wit lt . the more hear 1 y d eYery d1 cu y- . 1 . 1 C 1· · . 1th wnc 1 uv ·er annihilates the pro nets the sarcastw vigour, w · . th notes to the "Ossemens Fos-of their exuberant t.an~y nNl t e elle des Poissons." Nor is it . , d tb "H1stoue a ur . s1les, an e . h t dmiration the sagacious reason~ 'bl t peruse wit ou a . h . h possi e o1 · h he was l e d t o determinations w hiC ' In t e ings. b'ty owf ncca ses have b een ac cepted by those who have fo1- maJOri y ' lowed him. .. . 'n his elaborate and valuable special work Meckel, Kostbn, I 11 d Hallmann, in his excellent essay on the Vertebrate Sku 'ahn b ilt on Cuvier's foundations, h T oral Bone ave u . . on t .e fe mtph and 1. n 's ome cases, bettering' his determinatiOns applying ur . er f' t' ·1 bones No one can study these h h 1 gues 0 par 1cu ar · of t e omo 0 . d bt that osseous skulls are con-works carefully an~ retai~a~ t~:uo·h he may, with Cuvier, give structed upon a uniformdp . ' e~t to the notion that it is, in but a hesitating and gru ging ass some sense, a modified vertebral column. III That criterion of the trut.1 1 or. f:a l sehood of the vehr't ekbr a'lt . .,. . •hich the Okenians do not t In I theory of the skull, for : h Cuvier seems to have sought in ne~essary to loofk, a~dh wd ~cy the investigations of the embry-vain has been urnis e . ' 1837 to the present time. ologists from the year d. f the visceral arches by The first step was the Iscovteryt' o of the mode of develop- . b d the demons ra Ion Reichert ; t e seco~ ' sses of the Verteb?"ata, by the remark-ment of the skull, In all cla . d . th " Vierter Bericht able researches of Rathke,. contain~ .. :~ bei e der U niversitat zu tiber das N aturwissenschafthche Semina I ·n te Rathke's KOnigsberg," which was ~ublished in 1839. ha:Iw;:a; have the statement of his conclusions at length, so t. k with that means of fairly com paring his mode of gmng to wor of Oken :- . . deducible from the "The following results, among .others, are · h' h have been detailed:- d , observations w IC . . f f. t 1 life the notochor ex- ,, (1.) At the earliest perwd o 00 a THE 'l'HEORY OL•' THE VER'rEBRATE RKULJJ. 291 tends backwards, as far as the end of the body ; forwards, only to the interspace between the auditory capsules. "(2.) The gelatinous investing mass, which, at first, seems only to constitute a band to the Tight and to the left of the notochord, forms around it, in the further course of development, a sheath, which ends in a point posteriorly. Anteriorly, it sends out two processes which underlie the lateral parts of the skull, but very soon coalesce for a longer or shorter distance. Posteriorly, the sheath* projects but little beyond the notochord; but, anteriorly, for a considerable distance, as far as the infundibulum. It sends upwards two plates, which embrace the futu~ central parts of the nervous system laterally, probably throughout their entire length. '' (3.) The investing mass of the notochord is the material out of which the vertebral column and a. great part of the skull, though not the whole skull, are developed. "(4.) The most essential part of a vertebra is its body. With the exception of a few cartilaginous fishes, the cartilaginous foundation of that body (the notochord having disappeared earlier or later), has the form of either a ring, or a 1Ja]f ring; or, as is the case among the Mammalia, forms a solid mass, having the form of the segment of a cylinder. Subordinate parts of the vertebra are the vertebral arches and transverse processes, together with the ribs, which all, at the time they take on a cartilaginous character, appear as rays of the body, though sometimes they are not developed at all. Only in rare cases (Petromyzon) are vertebral arches developed without \ertebral bodies; that part of the investing mass of the notochord which is, in other cases, applied to the formation of such bodies, acquiring only a membranous consistency. "(5.) From that part of the. investing n1ass of the cephalic part of the notochord, which consists of the antm·ior part of the sheath of the notochord and its anterior paired processes, aro developed the basi-occipital, the basi-sphenoid, and the ethmoid, so that the ethmoid is the 1nost anterior of the parts of the skeleton which take their origin from the investing mass of the notochord. The basi-occipital is formed in that part of this * Pcl'hn.ps with rare exceptio,ns, as in Fistularia tabacrrwiu. 1 ~ |
