STAGE 46 Age 4 d., 10 h.; length 9-12 mm.

Ext. Crit.: Edge of operculum becoming convex. Xanthophores appearing on eye and abdomen. *Intestine showing 2 - 2 ½ revolutions*. *Hindlimb bud visible for the first time*.

Int. Crit.: Dura-endocranial membrane surrounding entire brain; *cells of Purkinje differentiating in corpora cerebelli*. *Some spinal ganglion cells enlarging and equalling Rohon-Beard cells in tail region*. *Distal end of ductus endolymphaticus enlarged as saccus endolymphaticus*; canalis lateralis partially separated from utriculus by septum formation.

Beginning of chondrification of ear capsule with cupula anterior and posterior; *complete chondrification of visceral skeleton; formation of fen. subocularis and for. caroticum*. Anterior tip of notochord degenerating. *Anlage of forelimb atrium detached from ectoderm; first mesenchymal accumulation of forelimb anlage. Double-layered ectoderm over clearly defined mesenchymal masses of hindlimb rudiments. Occipito-vertebral artery formed. *4-5 mesonephric units distinguishable*.

Oesophagus free of yolk. Food appearing in intestinal tract.