to the fourteenth the whole process is ossified, and the space between the maxillæ closed except posteriorly, where the anterior palatine canal remains permanently patent; the component parts of the bone, however, are not united until a later date. There are two other cartilaginous foci from which ossification ensues, viz. the pterygo-palatine cartilage in the superior maxillary process, a delicate bar from which arise in part the pterygoid and palatine plates; and Meckel’s cartilage in the mandibular process for the production of the mandible and malleus. All the other facial bones are developed from membrane, more or less in connection with these bars. The vomer is ossified from a single nucleus appearing in the upper part of the ethmo-vomerine plate, about the ninth week; from this two laminæ are developed, which, passing downwards and forwards on either side of the middle line, embrace the septal cartilage. The amount of the osseous material increases from behind forwards, until at maturity a median osseous lamina remains which is grooved only anteriorly. The palate bone develops from a single centre appearing about the eighth week at the junction of the horizontal and perpendicular portions. The superior maxilla is supposed to arise from four separate foci of ossification, viz. for the alveolar arch, for the palate, for the orbito-malar portion, and for the naso-facial segment. All these are united together by the third month. It is unnecessary here to discuss the development of the _teeth_ beyond stating that the thickening of the epiblast covering the gums, which occurs as the earliest sign of the production of the milk teeth, is to be seen about the forty-fifth day, when as yet there are no signs of ossification of the maxilla, and by two and a half months a distinct involution filled with cells is evident. Calcification commences about the eighteenth week of intra-uterine life, and extending from crown to fang is usually not completed until from twelve to twenty months after birth. By the fifteenth week of embryonic life preparation is being made for the development of the first four permanent molars, and soon afterwards in the sixteenth week occur the inflections of the mucous membrane giving rise to the enamel organs for the twenty anterior permanent teeth; and from this period until the birth of the infant the germs of the twenty-four permanent teeth are passing through the various stages preparatory to calcification, so that at birth the child has not only twenty milk teeth with calcification nearly complete, but also the germs of twenty-four permanent teeth. Calcification commences in twelve of these latter during the first year of life, viz. in the first molars and the incisors, and spreads from the crown in which it starts to the fang. In the case of the incisors this process is not completed until the tenth year.[43] * * * * *