DEVELOPMENT OF THE HARD PALATE 



iem owing to a change in the position of the mandible due to the development 

 of its arch (Fig. 146 B). With the withdrawal of the tongue the edges of the 



Median palatine 

 process 



Lateral palatine 



process 

 Int. choance 



Oral cavity 



Med. palatine . 

 process 



Raphe of lat. 

 palatine process 



Nasal passage 

 Anlage of uvula 



A B 



FIG. 147. Dissections to show the development of the hard palate in pig embryos. A, ventral 

 view of palatine processes of a 22 mm. pig embryo, the mandible having been removed; B, same of 35 

 mm. embryo showing fusion of palatine processes. 



palatine folds are approximated and soon fuse, thus cutting off the nasal passages 



from the primitive oral cavity dorsad (Fig. 147 B). At the point in the median 



line where the lateral and median 



palatine processes meet, fusion is 



not complete, leaving the incisive 



fossa, and laterad between the 



two processes openings persist 



for some time, which are known 



as the incisive canals (of Sten- 



son). 



After the withdrawal of the 

 tongue, the lateral palatine pro- 

 cesses take up a horizontal posi- 

 tion and their edges are approxi- 

 mated, because the cells on the 

 ventral sides of the folds prolifer- 

 ate more rapidly than those of 

 the dorsal side (Schorr, Anat. 

 Hefte, Bd. 36, 1908). That the 



change in position of the palatine folds is not mechanical, but due to unequal 

 growth, may be seen in Fig. 149, a section through the palatine folds of a pig 



FIG. 148. The roof of the mouth of a human embryo 

 about two and a half months old, showing the develop- 

 ment of the palate. .g., processus globularis; p.g.', pala- 

 tine process of processus globularis; mx, maxillary pro- 

 cess; mx', palatine fold of maxillary process. Close to 

 the angle between this and the palatine process of the 

 processus globularis on each side, the primitive choanae. 

 (After His.) 



