DEVELOPMENT OF THE FACE. 



processes separate the buccal from the nasal cavities, forming the 

 roof of the one and the floor of the other (Fig. 7). The horizontal 

 palatal plates meet first in front; the process of fusion spreads 

 backwards, and by the end of the second month it is complete. 



premaxilla 



naso-pal. for. 



palatal proc. of max. 

 palatine foramen, 

 palatal proc. of palatine 



Fig. 9.— Showing the Hard Palate at birth. The premaxillary part is formed from 

 the Mesial Nasal Processes ; the remainder by the Palatal Plates of the Maxillary 

 Processes. 



The condition of cleft palate is due to a partial or sometimes a 

 complete failure of the process of fusion. 



Bones formed in each Maxillary Process. — The zygomatic 

 process of the temporal, the malar, and the greater part of 

 the superior maxillary are formed directly from the connective 

 tissue within the process. They are membrane-formed bones. 

 - Pterygo-palatine Bar. — Two other bones formed in this 

 process have quite a different history. The internal pterygoid 

 plate, which is originally a separate bone, and the palate, are 

 developed over cartilage. When the maxillary process grows 

 forwards from the base of the mandibular arch, it carries with it 

 a prolongation of the cartilaginous bar which forms the skeletal 

 basis of that arch. The cartilaginous bar is known as the 

 pterygo-palatine, and in the membrane over this bar the pterygoid 

 (internal pterygoid process) and palatal bones are developed (Fig. 

 10 A, B, C). From the posterior end of this bar is developed 

 the incus in mammals and the quadrate bone in birds and reptiles. 

 In birds and reptiles the lower jaw articulates with the quadrate 

 bone (Fig. 10 B), and on the quadrate the superior maxilla is 

 supported by the pterygoid and palate bones. In amphibians 

 the quadrate, pterygoid and palate form a continuous bar of 



