The structures involved in ocular accommodation were studied with scanning electron microscopy in 5-day old chicken. Particular attention was paid to the ciliary muscle that was found to be subdivided into an anterior and a posterior portion. Since the anterior portion inserted on the wall of canal of Schlemm, we postulate that it could somehow control the flow of aqueous humour. According to its insertions, the posterior muscle could stretch the choroid coat. Thus, changes in the refractive power of the eye would be brought about by an indirect mechanism.