NINETEEN FIGURESOur knowledge of the embryological development of the horse is f a r from being complete. Few niammals have had their pharyngeal regions thoroughly investigated, and the horse has been almost completely neglected. Present-day attention on the endocrinal secretions in the human has revived a i d vitalized the interest in the pharyngeal derivatives. Since the liorse is a high-typed ungulate, with many embryological and aiiatoniical structures in cominoii with man, it is hoped that the findings of this investigation may aid in a more accurate interpretation of what is revealed in the human. The literature, even 011 the general embryological development of the horse, contains few contributions. Ewart (%) reviews this literature, mentioiling such contributors as Hausmann, Huxley, Bonnet, and Martin, whose contributions were based largely on the early embryonic membranes, with practically nothing on organologp. Ewart ('15) was able to state the accurate age of a certain horse ernbr>-o as being twenty-one days old. His drawings of appropriately selected cross-sections of this stage and the description of the structures iiivolved uridoubtedIy make a worthy contribution, but he considered the pharynx only incidentally. Robinson and Gibson ( '17) described the recoiistruction model of Ewart's twenty-one-day embryo, and this account serves as a valuable aid in interpretiiig Emart's figures. Sisson ( '21) deals adequately with the gross anatomy of the adult horse, henct: this work is accepted as a standard text in many veterinary medical schools. 233