DEYELOPMENT OF THE FACE. 5 



superior maxilla in the 3rd month of foetal life, the maxillae 

 overlapping and almost completely excluding them from the face. 

 The nasal spine is formed by the premaxillae. 



In mammals generally the premaxillae are highly developed 

 and form the snout part of the face. In the higher Primates the 

 face becomes less elongated, less prognathous and the premaxillae 

 less developed. In the orang, for instance, the premaxillae are 

 distinctly seen on the face at birth '(Fig- 5), but as the permanent 

 canines begin to develop they fuse with the maxillae. 



ant. nares. ■ 

 left premaxilla —f^ / -JP— maxilla 



canine. 



Fig. 5. — Showing the suture on the face between the premaxilla and maxilla in the 

 skull of a young orang. 



In man each premaxilla is usually ossified by two centres, 

 placed side by side. Hence it sometimes happens in cleft palate 

 that the fissure appears, not between the canine and lateral 

 incisor, but between the lateral and middle incisor. In such 

 cases the two centres of the premaxilla have failed to unite and 

 the cleft occurs between them. The two premaxillae unite together 

 in the first year after birth. Their vestigial character in man is 

 due to the small size of his masticatory apparatus and consequent 

 retrogression in the development of the facial part of his skull. 



Naso-palatine Foramen. — The naso-palatine foramina are 

 formed where the mesial nasal and two maxillary processes unite 

 to form the palate (Fig. 9). In animals with well-developed pre- 

 maxillae the two naso-palatine (anterior palatine) foramina are 

 large, and through each passes the naso-palatine duct, which 

 allows a communication between the buccal and nasal cavities. 

 The odour of the food within the mouth thus reaches the organ 



