|Carnegie embryo 8171. Early lacunar stage (Stage 5b)|
Courtesy of Dr. Allen C. Enders
The Virtual Human Embryo is an online ressource based on the serially sectioned embryos in this collection and includes 3D reconstructions. It covers all 23 Carnegie stages in the first 8 weeks of embryonic development and cannot be too highly recommended.
|Carnegie Embryo 7801. Showing extraembryonic coelom (eec)|
and secondary yolk sac (sys) (Stage 6)
Courtesy of Dr.Allen C. Enders
They make two claims. First that representations in textbooks have become increasingly schematic. This is demonstrably true. Second that the descriptions in standard texts are often based on extrapolation to humans from animal models. It is hard to assess if the latter truly is the case. For example Human Embryology by Hamilton, Boyd and Mossman (previous post) was based on the human embryos in the possession of the three authors. In Germany there was a strong tradition to cover the embryology of all vertebrates, concluding with the human, exemplified by Dietrich Starck's Embryologie.
In physiology, on the other hand, animal data often are presented as if they were human. One example concerns oxygen tensions in various parts of the fetal circulation. Pretty much every textbook of physiology has a large illustration of the fetal circulation with data obtained in sheep by Dawes, Mott and Widdicombe. The figure legends often fail to acknowledge the source or the species or both.