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 a portion 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 300 sections. The screen consists of three frames, a photographic frame on the upper left, a text frame on the lower left, and an orientation frame on the right. The photographic frame contains a photomicrographic image of a cross section of a 33 hour chick embryo taken from a set of 300 serial cross sections. The photographs are numbered one to 15 out of a possible 15.