At birth and in infancy the bone presents a much greater proportion from before back wards than vertically : its nasal process is long, its orbitar plate large, the antrum is already distinct, the tuberosity prominent, and there are some remarkable holes behind the incisor teeth, which are said to have an important connexion with the development of the second set of teeth.
In the adult the increase in the vertical di mensions corresponds with the developement of the antrum and alveolar border. In old age the alveoli are obliterated, the border con tracts, and the jaw diminishes in height. In the small vertical diameter the senile and in fantile upper jaw bear a resemblance to each other.
In the inferior mammalia, the maxillary bones are separated anteriorly in the middle line by a bone called os interrnaxillare or incisivum, which contains the superior incisor teeth when they are present; sometimes this bone is distinctly divisible into two by suture. This bone is present, although the superior incisors be absent, as in Ruminants and Eden tata, but in such cases is very small: on the other hand, when the incisor teeth are largely developed, it is of considerable size, as in the Rodentia. In the mature human fmtus no sign of this bone exists, but in examining the skulls of fmtuses about the third or fourth month of pregnancy, we observe it perfectly distinct from the maxillary bone. It sometimes happens that at more advanced periods, whether of in.. tra or extra-uterine life, evidence of the separa tion of the intermaxillary bone exists, and as I1Ieckel says, we often find a transverse narrow " lacuna" on the vault of the palate, extending from the external incisor tooth to the anterior palatine foramen. According to Weber, how ever, who examined the extensive collection of fmtal skeletons belonging to Professor Ilg in Prague, the intermaxillary bone was distinct only in those that had a double hare-lip. lie considers, however, that the intermaxillary bone readily separates when the skull of a child of one or two years old is placed for some time in dilute muriatic acid.* The palate bones, (ossa palatina ; Germ.
die Satimenbeine,) situated at the back part of the nose and roof of the mouth, locked be tween the maxillary bones and pterygoid pro cesses of the sphenoid, consist of two thin plates, one short and horizontal, the palatine ; the other long and vertical, the nasal. The
palatine process, or plate, has two surfaces and four borders. The upper surface, or the nasal, is smooth and concave, and forms the posterior fourth of the floor of the nose. The lower sur face, the palatine, rough, and slightly concave anteriorly, has on its posterior and outer part a transverse crest with a depression behind it for the attachment of the circumflexus palati muscle. In front and to the outer side of this is the inferior orifice of the posterior palatine canal, behind which are two or three small openings called accessory palatine holes, and in front of it is the commencement of the groove which lodges the posterior palatine vessels and nerves.
The anterior border is cut obliquely from below upwards and forwards, and rests on the posterior border of the palatine plate of the upper maxillary bone, forming with it the transverse palato-maxillary suture. The pos terior border, thin and concave, gives attach ment to the soft palate.
The internal border, rough and thick, is united to its fellow of the opposite side ; above, it forms a gtooved crest, which receives a part of the vomer, and is continuous with a similar crest formed on the internal border of the palatine plate of the upper maxillary bone. Behind, this border terminates in a sharp point, which, in conjunction with the corres ponding projection of the opposite bone, forms the posterior nasal spine, to which the levator uvula: muscle is attached. The external border is continuous with the vertical plate.
The nasal process, or plate, has two surfaces and four borders. The internal or nasal pre sents, tracing it from below upwards, 1. a smooth concave surface, which forms part of the inferior meatus : 2. a horizontal crest, the inferior turbinated crest, for the attach ment of the inferior turbinatcd bone : 3. ano ther concave surface forming part of the mid dle meatus : 4. another horizontal crest (the superior turbinated crest), shorter than the former, for the attachment of the middle tur binated bone of the ethmoid. This surface is covered with the pituitary membrane.