Figure 12-9. Diagram comparing the early stages of development in a primitive rodent, the thirteen-striped ground squirrel, and in the mouse. A, B, and C. The thirteen-striped ground squirrel. ( After Mossman and Weisfeldt, 1935). D, E, and F. The mouse (Mus musculus). (A and B, x 24; C, x 8; D and E, x100; F, x 50.

Mossman, H.W., and L.A. Weisfeldt. 1939. The fetal membrances of a primitive rodent, the thirteen-striped ground squirrel. Amer. J. Anat. 64: 59-109.