The surface of the chorion is covered evenly with minute villi, constituting a diffuse non-deciduate placenta.
The embryo passes through three stages - (I) still enclosed within the egg and living on its own yolk; (2) free, within the vitelline mass, which is directly swallowed by the mouth; (3) there is no more vitelline mass, but the embryo is possessed of long external gills, which serve for an exchange of nutritive fluid through the maternal uterus, these gills functioning in the same way as the chorionic villi of the mammalian egg.
The interior of the rumen or paunch has no tags or villi on its surface, and there is no distinct psalterium or manyplies.
Toffs is largely developed, and the placenta, so far as known, is nondeciduate, the chorionic villi being either evenly diffused or collected in groups or cotyledons (in Pecora).
A thickened ring encircling the upper part, called coronary cushion (13) and the sole (15), are covered with numerous thickly-set 17 papillae or villi, and take the greatest share in the formation of the hoof; the intermediate part constituting the front and side of the foot (14), corresponding with the wall of the hoof, is covered with parallel, fine longitudinal laminae, which fit into corresponding depressions in the inner side of the horny hoof.