. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. EM BR YONIC DE VELOrMENT. 121 .n c mye nexion with the archenteron, they commence to extend dorsally and ventrally between the ectoderm and the in- ternal organs (Fig. 66). Meanwhile the cells forming the inner or visceral wall of the pouch adjacent to the noto- chord elongate transversely and longitudinally, and begin to form the plate-like muscle-fibres of the myotome. The cells producing these fibres are arranged in such a way that ench of them giv
. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. EM BR YONIC DE VELOrMENT. 121 .n c mye nexion with the archenteron, they commence to extend dorsally and ventrally between the ectoderm and the in- ternal organs (Fig. 66). Meanwhile the cells forming the inner or visceral wall of the pouch adjacent to the noto- chord elongate transversely and longitudinally, and begin to form the plate-like muscle-fibres of the myotome. The cells producing these fibres are arranged in such a way that ench of them gives rise ^Sl^^^^^^-lm to a muscle-fibre extending from the anterior to the pos- terior limit of a myotome.* The muscles are at first closely approximated to the notochord and project freely into the cavity of the pouch. Fig- 66. —Transverse section througli tlie middle ot tiie Ijodv of an emi)rvo, The latter gradually grows with ten pairs of somites, to show the 1 „ 1 .-1 •, ^ ^. „ closure of medullarv tube and tlie dorsal downwards, untd it meets ^^^ ^,^,„,^^, ^^^^^^ ^^ ^„^ mesodermic its fellow of the other side ; somites, (.^fter hatsjhek.) al. Alimentary canal, ch. Notochord, the two fuse together, and in the cells of which vacuoles liave corn- so the cavity is made con- '" to form. /..;/. Commencing for- -' mation of lonyitudmal muscle-plates trom tinUOUS from side to side, the cells forming the inner wall of the . somite, .Myocuclomic cavity. below the mtestine. When this occurs, the primarily single cavity of each archenteric pouch becomes divided into two portions; namely, a dorsal portion, the somite proper or luyoavl, and a ventral portion, the cccloni, by a transverse partition, which arises through a fusion between the parietal and. * Already in the embryo shown in Fig. 63 C, and even at a somewhat ear- lier stafje, the muscles are so far developed that the body can be bent and jerked. By the time the mouth has broken through, muscu
Size: 1397px × 1789px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectfishes, bookyear1894
