Skull and Hyoid 235 



to form the horizontal plate, and more slowly upward to make the vertical plate. 

 Owing to the relative small vertical measurement of the nasal cavities at birth, asso- 

 ciated with the incomplete growth of the maxillae, the palate bone at this time shows a 

 vertical plate of only about the same length as the horizontal plate. 



THE HARD PALATE. 



The hard palate, as seen on the basal aspect of the skull, has its anterior two-thirds 

 to three-quarters made by the palatine plates of the maxillae, with the horizontal 

 plates of the palate bones forming the posterior third or fourth. It is bounded by 

 the alveolar process, which is highest at the sides. The region is concave as a whole 

 in all directions. The anterior palatine foramen is just behind the incisor region ; 

 this is covered by the incisive papilla in the recent state. Behind this the palate is 

 rough and has the mucous membrane firmly adherent to it the membrane becomes 

 thicker further back and leaves the bone smoother, although there are more abundant 

 glands in this situation. 



The (large) posterior palatine foramen is seen immediately internal to the alveolus 

 of the last molar tooth, and the suture line between maxilla and palate turns sharply 

 back along the alveolus to run into the foramen, indicating that the canal is made by 

 the articulation of the two bones. The main posterior palatine vessels and nerve 

 emerge here and turn forward toward the anterior palatine foramen, through which 

 the artery turns up on to the septum. The groove containing the structures is fre- 

 quently double, in which case the artery occupies the groove nearer the alveolus. 

 Behind the main opening another or perhaps two are visible ; these are for smaller 

 nerves and vessels belonging to the same group but turning back into the soft palate. 

 The aponeurosis of the Tensor palati reaches a ridge which runs transversely between 

 the foramina. In this region the lower surface of the horizontal plate of the palate can 

 be seen to pass directly into the lower surface of the tuberosity, behind the foramina. 

 The posterior edge is thin and concave, being prolonged centrally into a posterior 

 nasal spine. 



The region of the palatine suture is occasionally raised in the whole or part of its 

 length into a prominent ridge, known as the torus palatinus. A variety of palate 

 is rarely seen in which the maxillae are produced backwards between the palate bones 

 centrally. The commonest abnormality of the palate is " cleft palate," in which the 

 two palate-folds have failed to unite with each other, and if the cleft is complete, and 

 extends to the face, the fold at fault has also failed in union with the fronto-nasal 

 process : such failure may be on one or both sides. Fig. 186 shows how the deformity 

 can occur, and it is evident that if the folds fail to meet the bones cannot join 

 subsequently. 



As already mentioned, the secondary down-growths of the hinder walls of the alveoli of the 

 incisor region, toward the anterior palatine foramen, make the surface of this part of the bony 

 palate, and one or other of these processes may fail to unite with its neighbour : this leads to the 

 presence of a fissure extending out from the foramen. Such a fissure may appear between the 

 incisors, or to the outer side of the lateral incisor, or in rare cases even to the outer side of the canine- 

 The fissure was for many years considered to mark the limit of the " premaxilla," but its irregu- 

 larity of position, and the fact that it has even been seen doubled on one or both sides, was suffi- 

 cient argument against this view, and now it is known to be of quite secondary origin, as described. 

 It is of historical interest to note, also, that the presence of these fissures at one time led to the 

 adoption by many of the suggestion that the alveolar portion of the upper jaw resulted from the 

 fusion of three distinct parts, the endognathion, placed on the inner nasal process and carrying the 

 central incisor, the mesognathion on the lateral process bearing the lateral incisor, and the exo- 

 gnathion further out. There is, of course, no justification in development for this view, which was 



