T he present paper is intended to be the first of a series on the Anatomy of the Vertebrate Skull; and I have chosen the cranium and face of the Ostriches as a startingpoint, principally because of the mid position of these birds in the vertebrate subkingdom, and, in some degree also, because of their generalized character. Indeed, to any one familiar, on the one hand, with the structure of the skull in the higher mammalian types, and on the other with that of the osseous fishes, the skull of an Ostrich is interesting and important in a very high degree; serving, at it does, as a key to open up the meaning of parts so extremely unlike as the true homologues in the Fish and in the Mammal often are. And further, whilst aiding the anatomist in revealing the true morphological counterparts in the highest, as compared with the lowest types, the skull of an ostrich does also form a link of the utmost value for connecting together that of a cold-blooded and that of a warm-blooded creature.