. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. THE MEDULLARY GROOVE 69 from a model of the Beneke embryo, detached from the chorion by cutting through the belly-stalk, and with the roof of the amniotic cavity removed. The dorsal surface of the embryo, thus exposed, is an oval disk, resting, as it were, on the yolk-sac, and quite smooth except for a slight longitudinal groove upon its posterior portion. This is the primitive groove and sections passing through it show the primitive streak, consisting of a sheet of mesoderm interposed betwe
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. THE MEDULLARY GROOVE 69 from a model of the Beneke embryo, detached from the chorion by cutting through the belly-stalk, and with the roof of the amniotic cavity removed. The dorsal surface of the embryo, thus exposed, is an oval disk, resting, as it were, on the yolk-sac, and quite smooth except for a slight longitudinal groove upon its posterior portion. This is the primitive groove and sections passing through it show the primitive streak, consisting of a sheet of mesoderm interposed between the ectoderm and endoderm, as in the Peters embryo, and but poorly defined from the other two layers. From its anterior edge a median process extends forward for a short distance and is the head process (see p. 56). In front and to the sides of this there is as yet no mesoderm intervening between the ectoderm and Fig. 41.—Embryo from the Frassi Ovum, the Roof of the Amniotic Cavity having been removed. From a model, b, belly-stalk; , primitive groove; mg, medullary groove; n, neuren- teric canal.—(Frassi.) The embryonic disk of the Beneke embryo measured mm. in length. That of an embryo described by Frassi (Fig. 41) was mm. in length, and in correspondence with its greater size, it presents some advances in structure that are of interest. As in the younger embryo one sees a distinct primitive groove on the posterior portion of the embryonic disk, but the groove terminates anteriorly at a distinct pore (w), which perforates the disk and opens ventrally into the yolk-sac. This is the neurenteric canal (see p. 58) and in front of it a groove extends forward in the median line almost to the anterior edge of the embryonic disk and is evidently the first. 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
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Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectembryology
