STAGE 48 Age 7 ½ d.; length 14-17 mm.

Ext. Crit.: Beginning of pigmentation around n. acusticus. *Forelimb bud visible for the first time*. Shining gold-colored abdomen. *Hindlimb bud semicircular in lateral aspect*.

Int. Crit.: *Peripheral nuclear layer well differentiated in rostral part of optic tectum*; ecto- and endomeninx separated by interjacent membrane at level of mesencephalon. Spinal nerves 2, 3 and 4 reaching forelimb anlage; spinal nerves 8, 9 and 10 reaching hindlimb anlage. Beginning of formation of saccus perilymphaticus.

*Connection between ear capsule and parachordalia cartilaginous*; anlagen of arytenoids well defined mesenchymatous condensations. *Basal portions of atlas arches and 3^rd and 4^th vertebral arches procartilaginous*. *Trunk somite 1 disappeared*. Elastica externa and interna beginning to thicken in tail region. Forelimb rudiment a well defined mesenchymal bud covered by thickened epithelium of atrium. *Medial postcardinals fused as interrenal vein as far as junction with posterior vena cava; lateral postcardinals completed, opening into interrenal vein at level of cloaca*; mesonephric sinus formed. *First 6-8 pairs of mesonephric tubules coiling; 2-3 pairs of communicating with Wolffian ducts*; first nephrostomes appearing on ventral surface of mesonephros.

First taste buds appearing in roof of oro-pharyngeal cavity; thyroid gland consisting of 4-6 diffuse lobes. *Yolk completely disappeared from alimentary canal*.