210 



1-ACE. 



this period, and often much later, two renuivk- 

 able fissures. 1. The incisive fissure, which 

 may be traced from the alveolar border be- 

 tween the canine and lateral incisor tooth 

 backwards and upwards, along the incisive 

 canal towards the nasal process : it is sel- 

 dom observable on the facial surface of the 

 bone. The part of the bone circumscribed by 

 this fissure appears to correspond to the inter- 

 maxillary bone of animals, and is probably 

 developed as a separate piece : it supports the 

 mcisor teeth. 2. A fissure is often found ex- 

 tending from the infra-orbitar groove forwards 

 to the orifice of the canal. The existence of 

 these fissures has led some anatomists to sup- 

 pose that the bone is developed by these ossific 

 points. 



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 intermaxillare 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 fetus no sign 

 of this bone exists, but in examining the skulls 

 of foetuses 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 

 Meckel 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 

 foetal skeletons belonging to Professor Ilg in 

 Prague, the intermaxillary bone was distinct 

 only in those that had a double hare-lip. He 

 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.* 



T/ie palate bones, (ossa palatinu ; Germ. 



* Sec Weber in Froriep's Votizen, 1820, quoted 

 in Hildebrandl's Anatomic, II. ii. S. 95. 



(tii- Siiuiiienlieine,) 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 pnlutinc ; 

 the other long and vertical, the numil. 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 hates, 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 

 uvulse 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 turbinated 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. 



The external or zygomata-maxillary surface 

 is rough in front, where it rests against the 

 upper maxillary bone ; behind this the lower 

 two-thirds are marked by a groove, which, in 

 conjunction with one on the upper maxillary 

 bone, forms the posterior palatine canal. 

 Above this, the bone is smooth, and forms the 

 inner and deep part of the pterygo-maxillary 

 fissure. 



The anterior border, thin and projecting, 

 forms a process (the maxillary) which is re- 

 ceived into the fissure in the lower edge of the 

 orifice of the maxillary sinus. 



The posterior or pterygoid border is united 

 to the anterior border of the pterygoid process 

 of the sphenoid : below, it becomes broad 

 and is continued along a process which stands 



