To determine whether or not the alleged early obliteration of the facial division between the maxillary and premaxillary bones in man may be regarded as a definite human specific character, the form, structure, and relations of the premaxilla, and the period of obliteration of the facial portion of the premax. suture in man and the other Primates were studied in approximately 10,000 crania, including some 42 of the less frequently studied human races. The form of the premaxilla in man at the end of the 3d fetal mo. was almost identical with that of the anthropoids; immediately thereafter the ant. wall of the body of the premaxilla became overgrown by the lateral plates of the maxilla, and was, with the exception of the ant. nasal spine and the inf. portions of the pyriform aperture, completely absorbed and replaced by them. Only in this peculiar process of obliteration of the facial portion of the premaxilla in man may a specific character be recognized. The peculiar involution of the premaxilla in man is a necessary adaptation following upon the extreme reduction of the olfactory and oral senses, in association with the great reduction in the size of the anterior teeth.[long dash]The apical portion of the premaxilla may be seen upon the facial aspect of the late fetal and infant human skull in a fair proportion of cases separated from the maxilla by a distinct suture. In skulls over 6 yrs. of age the suture is never to be seen facially, though it may be seen endofacially, to a greater or less extent, in some 26% of cases. In the Primates as a whole the period at which the premax. suture tends to undergo obliteration is correlated with the size of the premaxilla; the smaller this size the earlier does the suture tend to undergo obliteration. Thus, negro fetuses, which are distinctly more prognathic than white fetuses, show a strong tendency for the vestiges of the premax. suture to remain unobliterated longer than in the more orthognathic white fetuses. The early union of the maxilla with the premaxilla is in no way connected with the period in the phylogenetic history of the species during which the peculiar characters of the premaxilla were acquired, but is the expression, rather, of early functional demands.[long dash]The naso-maxillary relations of the premaxilla are described, and are shown to be substantially the same in all Primates, including man.[long dash]A hitherto unrecognized, but constantly found, bone situated at the apex of the ascending or naso-maxillary process of the premaxilla, between the nasal bone medially and the frontal process of the maxilla laterally, in infant-young Old World monkeys is described as the "naso-maxillary" bone. Ignorance of the existence of this bone has led to the inaccurate description of the frontal relations of the premaxilla in Old World monkeys. This bone is also descr. in a few young human crania. It is considered to be the vestigial homologue of the similar element in Old World monkeys. It was not found in anthropoids, though it may be present in them. A review of the literature includes 118 titles.