DEVELOPMENT OF THE FACE 



831 



In the very first stages of development of the head, there is no 

 appearance of the face. The cephalic extremity consists simply of the 

 cerebral vesicles, the surface of this enlarged portion of the embryo 

 being covered, in front as well as behind, by the epiblast. During the 

 sixth week, after the cavity of the pharynx has appeared, the membrane 

 gives way in front, forming a large opening, which may be called the 

 first opening of the mouth. At this time, however, the face is open in 



Fig. 238. Mouth of a human embryo of thirty- 

 Jive days (Coste) . 



I, frontal process, widely sloped at its inferior 

 portion ; 2, 2, incisor processes produced by this 

 sloping; 3,3, nostrils; 4, lower lip and maxilla, 

 formed by the union of the inferior maxillary 

 processes; 5, 5, superior maxillary processes, 

 contiguous to the incisor process ; 6, mouth, still 

 confounded with the nasal fossae ; 7, first appear- 

 ance of the closure of the nasal fossae; 8, 8, first 

 appearance of the two halves of the palatine 

 arch; 9, tongue; 10, 10, eyes; n, 12, 13, visceral 

 arches. 



Fig. 239. Mouth of an embryo of forty days 

 (Coste). 



I, first appearance of the nose ; 2, 2, first ap- 

 pearance of the alae of the nose ; 3, appearance of 

 the closure beneath the nose ; 4, middle, or median 

 portion of the upper lip, formed by the approach 

 and union of the two incisor processes, a little 

 notch in the median line still indicating the primi- 

 tive separation of the two processes ; 5, 5, superior 

 maxillary processes, forming the lateral portions 

 of the upper lip ; 6, 6, groove for the develop- 

 ment of the lachrymal sac and the nasal canal ; 

 7, lower lip ; 8, mouth ; 9, 9, the two lateral halves 

 of the palatine arch, already nearly approximated 

 to each other in front, but still widely separated 

 behind. 



front as far back as the ears. The first, or superior visceral arch, 

 now appears as a projection of the mesoblast, extending forward. This 

 is soon marked by two secondary projections, the upper projection 

 forming the superior maxillary portion of the face, and the lower, the 

 inferior maxilla. The two projections that form the lower jaw soon 

 meet in the median line, and their superior margin is the lower lip. At 

 the same time there is a projection from above, extending between the 



