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In two previous papers, which are now i n the press, the authors have studied the development of the chondrocranium and the morphology of the fully formed chondrocranium of the Egyptian gecko, Ptyodactylus hasselquistii. The present paper, which is a continuation of the previous two, deals with the osteocranium of a late embryo of Ptyodactylus hasselquistii.Alizarine transparencies of some late embryos of Ptyodactylus, which were about to hatch, were prepared according to Hollister's method ('34). Each one of these embryos was 45 days old and had a total body length of 46 mm. These embryos were put in alizarine stain for about 48 hours, then washed with a 2% solution of KOH for about three weeks. After careful dissection under the binocular microscope, they were dehydrated in alcohol, cleared in xylol and mounted in Balsam. By this method the bone only was stained deep red, while the other tissues became more or less colorless. Dorsal, ventral and lateral views of the skull, as well as outer and inner views of the lower jaw were drawn by means of the camera lucida.At the same time, some embryos-having lengths and ages similar to those prepared by Hollister's method, and slightly younger than them-were stained in toto with Borax carmine. After sectioning, the transverse sections were counterstained with picroindigo-carmine. These sections helped the authors in clearing up several details.In this paper, attention is given to the relation of the bones to the adjacent cartilages of the chondrocranium, and to the topographical relation of the bones to each other in the late embryonic state. The adult skull of Ptyodactylus husselquistii is described by El-Toubi and Khalil ('52).

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