. The elements of Embryology. Embryology. X.] THE HUMAN EMBRYO. 339 The embryo is still but incompletely folded off from the yolk-sac below. In a still older stage the cranial flexure becomes still more pronounced, placing the mid-brain at the end of the long axis of the body. The body also begins to be ventrally curved (Fig. 110 C). Externally human embryos at this age are charac- terized by the small size of the anterior end of the head. The flexure goes on gradually increasing, and in the third week of pregnancy in embryos of about 4 mm. the limbs make their appearance. The embryo at this s
. The elements of Embryology. Embryology. X.] THE HUMAN EMBRYO. 339 The embryo is still but incompletely folded off from the yolk-sac below. In a still older stage the cranial flexure becomes still more pronounced, placing the mid-brain at the end of the long axis of the body. The body also begins to be ventrally curved (Fig. 110 C). Externally human embryos at this age are charac- terized by the small size of the anterior end of the head. The flexure goes on gradually increasing, and in the third week of pregnancy in embryos of about 4 mm. the limbs make their appearance. The embryo at this stage (Fig. 112), which is about Fig. Two VIEWS OF A Human Embryo of between the Third AND Fourth Week. A. Side view. (From KoUiker; after Allen Thomson.) a. amnion; b. umbilical vesicle; c. mandibular arch; e. hyoid arch; /. commencing anterior Umb; g. primitive auditory vesicle; h. eye; i. heart. B. Dorsal view to shew the attachment of the dilated allantoic stalk to the chorion. (From a sketch by Allen Thomson.) am. amnion; all. allantois ; ys. yolk-sac. 22—2. 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 Foster, M. (Michael), Sir, 1836-1907. London, MacMillan
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