DEVELOPMENT OF THE FACE. 



827 



sides of the head and present anteriorly, until finally their axes become parallel. 

 These processes advance from the two sides, come to the sides of the incisor 

 process, beneath the nose, unite with the incisor process on either side, and 

 their lower margin, with the lower margin of the incisor process, forms the 

 upper lip ; but before this, the two lateral halves of the incisor process have 

 united in the median line. At the bottom of the cavity of the mouth a 

 small papilla makes its appearance, which gradually elongates and forms the 

 tongue. 



While this process of development of the anterior portion of the first 

 visceral arch is going on, at its posterior portion, the malleus and incus are 

 developing, the former being at first connected with the cai'tilage of Meckel, 

 which extends along the inner surface of the inferior maxilla, the cartilages 

 from either side meeting at the chin. The cleft between the first and the 

 second visceral arch has closed, except at its posterior portion, where an 

 opening is left for 

 the external audi- 

 tory meatus, the 

 cavity of the tym- 

 panum and the 

 Eustachian tube. 



At the same 

 time the second vis- 

 ceral arch advances 

 and forms the 

 stapes, the styloid 

 ligament and the 

 lesser cornua of the 

 hyoid bone. The 

 third arch advances 

 in the same way ; 

 and the arches from 

 the two sides meet, 

 become united in 

 the median line and 

 form the body and 

 the greater cornua 

 of the hyoid bone. 

 The clefts between 

 the second and the 

 third and between 

 the third and 

 fourth arches 



\ 



are 



FIG. 308. Mouth of a human em- 

 bryon of thirty-five, days (Coste). 



1, frontal process, widely sloped at 

 its inferior portion ; 2, 2, inci- 

 sor 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 max- 

 illary processes, contiguous to 

 the incisor process ; 6, mouth, 

 still confounded with the nasal 

 fossae ; 7, first appearance of 

 the closure of the nasal fossae ; 

 8, 8, first appearance of the two 

 halves of the palatine arch ; 9, 

 tongue ; 10. 10, eyes ; 11, 12, 13, 

 visceral arches. 



FIG. 309. Mouth of an embryon of for- 

 ty days (Coste). 



1, first appearance of the nose ; 2, 2, first 

 appearance of the alae of the nose ; 

 3, appearance of the closure beneath 

 the nose ; 4, middle, or median por- 

 tion of the upper lip, formed by the 

 approach and union of the two in- 

 cisor processes, a little notch in the 

 median line still indicating the prim- 

 itive separation of the two process- 

 es; 5, 5, superior maxillary process- 

 es, forming the lateral portions of 

 the upper lip r. 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. 



finally obliterated. 



The fourth arch forms the sides of the neck and the larynx, the arytenoid 

 cartilages being developed first. In front of the larynx and just behind the 

 tongue, is a little elevation, which is developed into the epiglottis. The 



