. The development of the chick; an introduction to embryology. Birds -- Embryology. 422 THE DEVELOPMENT OF THE CHICK and membrane bones of the skull before it begins in the vertebrae. It takes place in antero-posterior order, so that a series of stages may be followed in a single embryo (cf. Fig. 242). There are three main centers for each vertebra, viz., one in the body and one in each neural arch. The ossification of the centrum is almost J!i^-\ t "* "si-"'- :' 1 ? /v. ,¥edob/ UB-^'^ \. I'V^ "-^'il Sod-4?•'^•<, '^ ^PV4 Fig. 239. — Lateral
. The development of the chick; an introduction to embryology. Birds -- Embryology. 422 THE DEVELOPMENT OF THE CHICK and membrane bones of the skull before it begins in the vertebrae. It takes place in antero-posterior order, so that a series of stages may be followed in a single embryo (cf. Fig. 242). There are three main centers for each vertebra, viz., one in the body and one in each neural arch. The ossification of the centrum is almost J!i^-\ t "* "si-"'- :' 1 ? /v. ,¥edob/ UB-^'^ \. I'V^ "-^'il Sod-4?•'^•<, '^ ^PV4 Fig. 239. — Lateral sagittal section of the same vertebrae (as in Fig. 238). At. 1, 2, Floor and roof of atlas. B. C, Basis cranii. Cerv. n. 1, 2, First and second cervical nerves. Med. Obi., Medulla oblongata. R. V. 2, 3, 4, Ribs of the second, third, and fourth vertebrae. V. A. 2, 3, Arches of the second and third vertebrae. XII 2, Second root of hypoglossus. entirely endochondral, though traces of perichondral ossification may be found on the ventral and dorsal surfaces of each centrum before the endochondral ossification sets in. The perichondral centers soon cease activity. The endochondral centers arise just outside the perichordal sheath near the center of each ver- tebra on each side of the middle line, but soon fuse around the. 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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