The study of serial sections allows for the study of the microscopic anatomy of the embryo, in particular, the internal anatomy of the embryo. Many features that are not evident in the study of the whole embryo can be examined by viewing a sequence of sections of the embryo.
Serial sections consist of the entire embryo sectioned in a certain plane.
In the case of serial cross sections, the entire embryo was sectioned perpendicularly to the cranio-caudal axis from the beginning of the head to the end of the tail and all the sections were laid out in sequence on microscope slides. The embryo from which the accompanying photomicrographs were taken consisted of 336 sections. At a thickness of approximately 12 micrometers per section, the embryo was 4,800 micrometers or 4.8 millimeters in length. The screen consists of three frames, a photographic frame on the left, a text frame on the upper right, and an orientation frame on the lower right. The photographic frame contains a photomicrographic image of a cross section of a 5-7 mm frog embryo taken from a set of 400 serial cross sections.