. The development of the chick; an introduction to embryology . )oints ( and d (;. 78 C). Study of the fusion of the amniotic folds in actual sectionsshows, that the line of fusion of the ojiposite amniotic limbs isover tlie doisal surface of the embryo only so long as the latterlies flat on the yolk; it does not follow the turning of the embryoon to its left side, and the consequence is that, after rotation ofthe embryo, the line of fusion lies over the upper (right) side ofthe embr^o, often opposite the liorizontal level of the intestine(Fig. 79). Thus one fold of the amnion passes all t
. The development of the chick; an introduction to embryology . )oints ( and d (;. 78 C). Study of the fusion of the amniotic folds in actual sectionsshows, that the line of fusion of the ojiposite amniotic limbs isover tlie doisal surface of the embryo only so long as the latterlies flat on the yolk; it does not follow the turning of the embryoon to its left side, and the consequence is that, after rotation ofthe embryo, the line of fusion lies over the upper (right) side ofthe embr^o, often opposite the liorizontal level of the intestine(Fig. 79). Thus one fold of the amnion passes all the way fromthe under side over the back of the embiyo and around on theother side to the line of fusion, and thus is several times as longas the opposite limb. Moreover, the amniotic fold of the right Fig. 79. — Section of an embryo of about 60 luiurs to show the sec-ondary fold (s. f.) of the amnion on the right a., Ectanniion. s. £., Secondary fold. 1., Left, r., Right. side is invariably thicker than that of the left side, and is alwaysthrown into secondary folds at the }ilace of turning (Fig. 79).These conditions are satisfactorily explained, as noted above, bythe mere ttirning of the embryo on its siile. One nuist therefore distinguish in the upjuM- liml) of the aiu-nion two kinds of folds: (1) The oidinary amniotic fold inducedby the fusion of the right and left folds, and (2) secondary foldsformed simply by the ])r()cess of twisting of the embryo. These secontlary folds of the amnion are very transitory,except in two regions: (1) Above the hind end of the heart (apexof ventiicle). and continuing a short distance behind it; (2) inthe region immediately in front of the allantois, at sixty to seventyhours, thus in the neighborhood of the final closure of the amnioti
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