DEVELOPMENT OF THE FACE 



147 



fused early to form the lower jaw. Laterally, the frontal process of the 

 head is early divided into lateral and median nasal processes by the develop- 

 ment of the olfactory pits. These processes are distinct and most promi- 

 nent at 12 mm. (Fig. 149 A). Soon, in 13 to 14 mm. embryos, the median 

 nasal processes fuse with the maxillary processes of the first arch and con- 

 stitute the upper jaw (Fig. 149 B). The lateral nasal processes fuse with 



FIG. 150. Development of the face of the human embryo (His). A, Embryo of 8 mm. 

 (X 7.5); the median frontal process differentiating into median nasal processes, or processes 

 globulares, toward which the maxillary processes of the first branchial arch are extending. B, 

 Embryo of 13.7 mm. (X 5); the globular, lateral nasal and maxillary processes are in apposi- 

 tion; the primitive naris is now better defined. C, Embryo of 17 mm. (X 5); immediate 

 boundaries of mouth are more definite and the nasal orifices are partly formed, the external 

 ear appearing. D, Embryo of nearly eight weeks (X 5). 



the maxillary processes and form the cheeks, the lateral part of the Up, 

 and the alee of the nose. Later, the median nasal processes unite and be- 

 come the median part of the upper lip. Meanwhile, the mesial remainder 

 of the original frontal process (Fig. 149 A) is compressed and becomes the 

 septum and dorsum of the nose. The development of the olfactory organ 

 will be traced on p. 371. 



