Embryology of the sheep. I. Extraembryonic membranes and the development of body form

Abstract The developmental anatomy of the sheep in the early prenatal period (14 to 34 days) was studied using embryos of known coital age, and embryos of known size with estimated coital age. Characteristics of the embryos were studied by gross observation under the dissecting microscope, and by means of serial sections. The period of the ovum (from conception to 10 days) and the early embryonic period (from 11 to 14 days) are summarized from the literature. This work provides a detailed, systematic account of embryonic development in the sheep and establishes size‐age standards. Anatomical features encountered in the normal development of the sheep embryo are documented day‐by‐day because they are essential for studies of teratogenesis and early prenatal mortality.