STAGE 53 Age +/- 24 d.; length 50-60 mm.

Ext. Crit.: *Fore- and hindlimbs in paddle stage*. *Hindlimb without foot somewhat longer than broad; 4^th and 5^th toe indicated*.

Int. Crit.: *"Stirnorgan" just cranial to level of lamina terminalis*; first development of granular layer from ependyma in cerebellum; *Purkinje layers fusing in dorsal midline*. N. trochlearis passing through canal in crista trabeculae. *Dorsal column extending into prebrachial levels of spinal cord*; descendance of lumbar ganglia started.

*Formation of canales olfactorii and tectum anterius*; beginning of formation of goniale; *beginning of chonrdification of arytenoids and annulus cricoideus*. *Chondrification of occipital arches completed; chondrification completed of 3^rd pair of vertebral arches*; perichordal tube beginning to chondrify anteriorly underneath vertebral arches; *ventral perichordal tube chondrified down to region of 4^th vertebra*. 10 pairs of mm. interarcuales distinguishable; pars externus superficialis of m. obliquus abdominis, and m. transversus abdominis developing. *Shoulder girdle divided into scapular and coracoidal portions*. Beginning of chondrification of pelvic girdle. *Femur chondrifying, tibia and fibula, tibiale and fibulare procartilaginous, skeleton of foot mesenchymatous*. Beginning of histogenesis of muscle fibers in thigh and leg. Congestion of pronephros.

Typhlosole extending into beginning of second revolution of outer intestinal spiral.