. On the anatomy of vertebrates [electronic resource] . from the oviduct additional layers, ib. A, b, which, either in com-bination with, or substitution for, the hyalinion, become themedium of applying the capillaries of the foetus to those of themother continued into the decidua. When the foetal appendageshave attained, in this Rodent, the stage they exhibit in the Mar-supial, fig. 569—viz. the formation of the amniotic bag, fig. 571, #,the inclosure of the unconverted germ-mass, or yolk, by a vascularvitellicle, b, and the out-budding of a small allantois, c—the em-bryo is by no means so fa
. On the anatomy of vertebrates [electronic resource] . from the oviduct additional layers, ib. A, b, which, either in com-bination with, or substitution for, the hyalinion, become themedium of applying the capillaries of the foetus to those of themother continued into the decidua. When the foetal appendageshave attained, in this Rodent, the stage they exhibit in the Mar-supial, fig. 569—viz. the formation of the amniotic bag, fig. 571, #,the inclosure of the unconverted germ-mass, or yolk, by a vascularvitellicle, b, and the out-budding of a small allantois, c—the em-bryo is by no means so far advanced. The ventral parietes of thethoracic-abdominal cavity are not formed, the bilocular heart is 1 In the indication of the various definable parts of this deciduous substance a voca-bulary of terms has been created ; e. g. non-plaeental uterine mucous membrane, ute-roplacental mucous membrane, i persistent, or non-deciduous serotina, deciduousserotina, fimbriae of decidua serotina, membrana decidua, decidua reflexa, rags, tags, &c. 571. Uterine ova, Rabbit, cccvnt. DEVELOPMENT OF LISSENCEPII ALA. 125 exterior to it; neither lungs nor diaphragm have yet appeared;the parallel columns of the neural axis indicate the primarybrain-vesicles, by receding from each other in the long cephalicexpansion ; a few pairs of protovertebras show their beginningsat the sides of the myelon, and there is no trace whatever oflimbs. The ovum has wholly sunk into a bed of the decidu-ously-developed lining substance of the womb. Before the Mar-supial stage of the foetus has been reached, changes have takenplace in the environment of the embryo, and the growth of theabdominal parietes having reduced the wide aperture, shownin fig. 571, C, to a navel, the embryo with its amnios hassunk into the vitellicle, the trunks of the vitelline artery andveins becoming concomitantly elongated. The allantois comesin contact with that part of the chorion beyond the e vena ter-minalis, and, having fulfill
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