A system of obstetrics . st and epiblast of the somatopleuric layer of the 1 The explanation of this character in the segmentation is not difficult to primary segmentation of the body is that of the muscle-plates, which were pres-ent in the primitive forms in which vertebrae had not appeared. As soon, however, a*the notochordal sheath was required to be strong as well as flexible, it necessarilybecame divided into a series of segments. The condition under which the lateral muscles can best cause the flexure of thevertebral column is clearly that each myotome [segment of longitudinal m
A system of obstetrics . st and epiblast of the somatopleuric layer of the 1 The explanation of this character in the segmentation is not difficult to primary segmentation of the body is that of the muscle-plates, which were pres-ent in the primitive forms in which vertebrae had not appeared. As soon, however, a*the notochordal sheath was required to be strong as well as flexible, it necessarilybecame divided into a series of segments. The condition under which the lateral muscles can best cause the flexure of thevertebral column is clearly that each myotome [segment of longitudinal muscle] shallbe capable of acting on two vertebrae; and this condition can only be fulfilled whenthe myotomes are opposite the intervals between the vertebras (Balfour). DEVELOPMENT OF ORGANS AXD SYSTEMS. 145 lateral plates at positions which correspond to the future pectoral andpelvic arches. They appear in the human embryo as somewhat flat-tened outgrowths about the fourth week after conception. If the dia- Fig. 72. Fig.
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
