DEVELOPMENT OF THE FACE. 



tions of this part. When, by an arrest of development, the 

 superior maxilla on one side fails to unite with the side of 

 the incisor process, we have the very common deformity 

 known as single hare-lip. If this union fail on both sides, 

 we have double hare-lip, when the incisor process is usually 

 more or less projecting. As a very rare deformity, it is 

 sometimes observed that the two sides of the incisor process 



FIG. 47. 



Fio. 48. 



Fig. 47. Month of a human embryon of thirty -five dayc. 1, 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 maxil- 

 lary processes, contiguous to the incisor process ; 6, mouth, still confounded with the nasal 

 fossae ; 7, appearance of the closure of the nasal fossae ; 8, 8, appearance of the two halves 

 of the palatine arch ; 9. tongue ; 10, 10, eyes; 11, 12, 13, visceral arches. (SAPPKT, Traite 

 cTanatomie, Paris, 1874, tome iv., p. 78.) 



Fig. 48. Mouth of an embryon of forty days. 1, first appearance of the nose; 2,2, first appear- 

 ance of the alee of the nose; 8, appearance of the closure beneath the nose; 4, middle, or me- 

 dian 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 primitive separation of the two processes ; 

 5, 5, superior maxillary processes, forming the lateral portions of the upper lip ; 6, 6, groove 

 for the development 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. (SAPPEY, Traite d'anatomie, Paris, 1874, tome iv., p. 78.) * 



1 The periods of development indicated for these diagrams are somewhat 

 earlier than those which we have quoted from Burdach ; but it is impossible to 

 fix these with absolute accuracy, and all the estimates given by authors are under- 

 stood to be merely approximative. 

 157 



