STAGE 55 Age +/- 32 d.; length 70-80 mm.

Ext. Crit.: *Hand pronated about 90°; free parts of fingers about equally long as broad*. *Length of hindlimb without foot about 3 x its breadth; length of cartilages of 4^th and 5^th toe about 4 x their breadth*.

Int. Crit.: *Lumbar motor column nuclei of spinal cord showing twice cross sectional area of adjacent non-motor nuclei*. *Cartilage present in medial portion of sclera of eye*. Ventro-lateral lobe of saccus endolymphaticus reaching from telencephalon to 2^nd spinal nerve.

*Fusion of cristae occipitales laterales with tectum posterior*. *11^th pair of vertebral arches chondrified*; chondrification of ventral perichordal tube extending over entire trunk region; *dorsal perichordal tube chondrified vertebrally down to 6^th pair, and intervertebrally down to 3^rd pair of vertebral arches*. Mesenchymatous perichordal tube of tail thickening. *Scapula, procordacoid and coracoid procartilaginous*. *Humerus procartilaginous*. Shoulder girdle musculature indicated. Upper arm musculature indicated. *Perichondral ossification of femur started*. All major muscles of thigh and leg present with both origins and insertions; foot musculature well defined. Signs of local degeneration in middle region of mesonephros; anlage of urinary bladder discernable. Small tubular cavities appearing in compact testis; medullary tissue of ovary largely excavated; *first meiotic division in ovary*. Single row of maxillary tooth germs developed.