DEVELOPMENT OF THE HARD PALATE 



155 



The external car is developed around the first branchial cleft by the appearance of small 

 tubercules which form the auricle. The cleft itself becomes the external auditory meatus and 

 the concha of the ear. (For the development of the external ear see Chapter XII). 



Fie. 145. — FJevelopment of the face of the human embryo (His). A, embryo of about twenty-nine 

 days. The median frontal process differentiating into median nasal processes or processus globulares, 

 toward which the maxillary processes of first visceral arch are extending. B, embryo of about thirty- 

 four days: the globular, lateral nasal, and maxillary processes are in apposition; the primitive naris is 

 now better defined. C, embryo of about the eighth week: immediate boundaries of mouth are more 

 definite and the nasal orifices are partly formed, external ear appearing. I), embryo at end of second 

 month. 



DEVELOPMENT OF THE HARD PALATE 

 This may be studied advantageously in pig embryos of two stages : (a) 20 

 to 25 mm. long; (b) 28 to 35 mm. long. In the first stage, the jaws are close 

 together and the mandible usually rests against the breast region. The palatine 

 processes are separated by the tongue and are directed ventrad (Fig. 146 A). 

 In embryos of 26 to 28 mm., the jaws open and the tongue lies ventral to the 

 palatine processes which now approach each other in a horizontal plane (Fig. 

 146 B). Dissections may be made by carrying a shallow incision from the 



