A scanning electron microscopic study of the normal development of the chick wing from stages 19 to 36. A supplement to the Hamburger and Hamilton staging system.

The purpose of a staging system is to stage embryos by morphology rather than chronology. This is particularly useful when embryos do not develop exactly synchronously, as in the case of the chick. At present the Hamburger and Hamilton (1951) series is universally used to stage chick embryos. The aim of the present study was to provide a series of morphological descriptions of the normal stages of development of the chick wing bud from stages 19 to 36, and to correct some errors of the original system which may be overlooked by those new to the chick wing bud as an experimental model, and who rely primarily on the Hamburger and Hamilton stage series. In addition, Summerbell's (1976) observations on the appearance of the cartilaginous elements made from alcian green-stained whole mounts have been correlated with the external appearance of the wing bud to provide a more complete understanding of the skeletal development that influences, and to some degree accounts for, the changes in external morphology. Scanning electron microscopy (SEM) has been used to obtain images of much greater resolution and detail than those available from Hamburger and Hamilton, whilst using comparable magnifications to those attainable using conventional dissecting microscopes. The number of somites across which the proximal part of the wing bud extends has been provided as a measure of the limb width at early stages (19-24). At certain stages there were clear differences between the characteristic wing bud features described by Hamburger and Hamilton and those observed in the present study.(ABSTRACT TRUNCATED AT 250 WORDS)