Carnegie Stage 13 Definition
Age is approximately 28 postovulatory days
Length is approximately 4-6 mm
External Features Include: all four limb buds are usually visible; otic vesicle is closed; lens disc is generally not indented.
(O'Rahilly R and Muller F [1987] Developmental
Stages in Human Embryos. Carnegie Institute, Washington, Publication
no. 637)