. The development of the chick; an introduction to embryology. Birds -- Embryology. THE SKELETON 417 a separate component. Schauinsland has interpreted it as the homologue of the hsemal arches of reptilia (, Sphenodon). The membrane represents not only the future bony parts but the Ugaments and periosteum as well. Hence we find that the successive membranous vertebrae are not separate structures but are united by membrane, , condensed mesenchyme, and are distinguishable from the future ligaments at first only by greater condensation. In the stage of Fig. 233, chondrification has alread
. The development of the chick; an introduction to embryology. Birds -- Embryology. THE SKELETON 417 a separate component. Schauinsland has interpreted it as the homologue of the hsemal arches of reptilia (, Sphenodon). The membrane represents not only the future bony parts but the Ugaments and periosteum as well. Hence we find that the successive membranous vertebrae are not separate structures but are united by membrane, , condensed mesenchyme, and are distinguishable from the future ligaments at first only by greater condensation. In the stage of Fig. 233, chondrification has already begun in the vertebral body, hence there is a sharp r "-v^r yy' Fig. 235. — Median sagittal section of the cervical region at the end of the sixth day of incubation. (After Froriep.) x 40. b. C, Basis cranii. i'v. L. 1, 2, 3, First, second, and third intervertebral Hgaments. s. n. b. 1, 2, 3,4, First, second, third, and fourth subnotochordal bars (hypocentra). v. C. 3, 4, Pleurocentra of third and fourth vertebrae. distinction in this region between the vertebral body and inter- vertebral discs. The centers of chondrification, however, grade into the membranous costal i)rocesses and neural arches. The vertebral segmentation has now become predominant as contrasted with the primitive somitic. The development of the vertebrae during the fifth day com- prises: (1) Fusion of successive caudal and cephalic divisions of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lillie, Frank Rattray, 1870-1947. New York, Holt
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