INTRODUCTION

The 3-4 mm Frog Embryo

Serial Sections

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 10 micrometers per section, the embryo was 3, 360 micrometers or 3.36 millimeters in length.

Navigation within the Web Site

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 screen is best viewed with the monitor display area set to 800 by 600 pixels.

The photographic frames contain photomicrographic images of cross sections of a 3-4 mm frog embryo taken from a set of 336 serial cross sections. The photographs are numbered one to 37 out of a possible 37. The cross sectional photographs are presented with the dorsal surface of the embryo uppermost and ventral surface lowermost. The lateral surfaces of the embryo are located on the right and left. A button below the photograph allows you to click and move to the following photograph.

The largest frame on the screen is the text frame. This frame has a scroll bar on the right hand side of the frame that allows you to move text upward and downward. The text consists of descriptive paragraphs that begin with a title that gives the section number out of the total number of 336 sections that comprise the embryo. A listing of the major visible features occurring at this particular level of sectioning follows the section number. Clicking on the title will bring the corresponding photograph into the photographic screen.

The orientation frame is located on the lower right hand side of the screen. This frame contains a thumbnail size diagram of a side view of a 3-4 mm frog embryo with a vertical line that indicates the level of sectioning of each cross sectional photograph. A button list, allows you to click and move to a previous section, the next section, the main menu, or the index.