. The development of the chick : an introduction to embryology. Embryology; Chickens -- Embryos. 420 THE DEVELOPMENT OF THE CHICK notochord runs continuously through the centra of the four vertebrae shown. It is constricted intravertebrally and expanded intervertebrally, so that the vertebral bodies are amphiccelous. The intervertebral discs are not shown. A pre- and postzygapo- physis is formed on each arch. It is by no means certain that the parts separated by the clear streak shown in the figure extending through centra and arches correspond to the sclerotomal com- ponents of the primitive
. The development of the chick : an introduction to embryology. Embryology; Chickens -- Embryos. 420 THE DEVELOPMENT OF THE CHICK notochord runs continuously through the centra of the four vertebrae shown. It is constricted intravertebrally and expanded intervertebrally, so that the vertebral bodies are amphiccelous. The intervertebral discs are not shown. A pre- and postzygapo- physis is formed on each arch. It is by no means certain that the parts separated by the clear streak shown in the figure extending through centra and arches correspond to the sclerotomal com- ponents of the primitive vertebrae, though this was the in- terpretation of Schauinsland as shown in the figure; further study seems necessary to determine the exact relations of the primitive sclerotomal components to the parts of the definitive vertebra. The successive vertebrae have persistent membranous. Fig. 237. —The right side of four bisected vertebrae of the trunk of an 8-day chick. (After Schauinsland.) caud. V. A., Caudal division of vertebral arch. ceph. v. A., Cephalic division of vertebral arch. N'ch., Notochord. connections in the regions of the neural spines, zygapophyses and centra. These are shown in Figs. 238 and 239 (cf. also Fig. 150); they are continuous with the perichondrium and all are derived from unchondrified parts of the original membran- ous vertebrae. Atlas and Axis (epistropheus). The first and second verte- brae agree with the others in the membranous stage. But, when chondrification sets in, the hypochordal bar of the first vertebra does not fuse with the body, but remains separate and forms its floor (Figs. 238 and 239). The body of the first vertebra chondrifies separately and is attached by membrane to the anterior end of the body of the second vertebra, representing in fact the odon- toid process of the latter. It has later a separate center of ossi- fication, but fuses subsequently with the body of the second vertebra, forming the odondoid process (Fig. 240).. P
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Keywords: ., bookauthorlilliefrankrat, bookcentury1900, booksubjectembryology
