The development of the human body; a manual of human embryology . til more than half the yolk-stalk has become enclosed within the umbilical cord. Theneck and sacral bends are still very pronounced, although * This measurement is taken in a straight line from the most anteriorportion of the neck bend to the middle point of the sacral bend and doesnot follow the curvature of the embryo. It may be spoken of as the neck-rump length and is convenient for use during the stages when the embryois coiled upon itself. 98 THE DEVELOPMENT OF THE HUMAN BODY. the embryo is beginning to straighten out and i
The development of the human body; a manual of human embryology . til more than half the yolk-stalk has become enclosed within the umbilical cord. Theneck and sacral bends are still very pronounced, although * This measurement is taken in a straight line from the most anteriorportion of the neck bend to the middle point of the sacral bend and doesnot follow the curvature of the embryo. It may be spoken of as the neck-rump length and is convenient for use during the stages when the embryois coiled upon itself. 98 THE DEVELOPMENT OF THE HUMAN BODY. the embryo is beginning to straighten out and is not quiteso much coiled as in the preceding stage. At the poste-rior end of the body there has developed a rather abruptlyconical tail filament, in the place of the blunt and gradu-ally tapering termination seen in earlier stages, and a well-marked rotundity of the abdomen, due to the rapidly in-creasing size of the liver, begins to become evident. In later stages the enclosure of the yolk- and belly-stalks within the umbilical cord proceeds until finally the. Fig. 48.—Embryo Br2, mm. Long.—(His.) cord is complete through the entire interval between theembryo and the wall of the ovum. At the same time thestraightening out of the embryo continues, as may be seenin Fig. 48 representing the embryo xlv (Br2) of His, whichshows also, both in front of and behind the neck bend, adistinct depression, the more anterior one being the occi-pital and the more posterior the neck depression; boththese depressions are the expressions of changes taking THE EXTERNAL FORM OF THE BODY. 99 place in the central nervous system. The tail filament hasbecome more marked, and in the head region a slightridge surrounding the eyeball and marking out the con-junctival area has appeared, a depression anterior to thenasal fossae marks off the nose from the forehead, andthe external ear, whose development willbe consideredlater on, has become quite distinct. This embryo had aneck-rump length of 13.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
