414: 



GENERATION. 



FIG. 46. 



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 cor- 

 mia of the hyoid. The clefts between the second and third 

 and between the third and fourth arches become obliterated 

 by the deposition of plastic matter. 



The fourth arch forms the sides of the neck and the lar- 

 ynx, 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. 



According to Bur- 

 dach, who has noted 

 with great accuracy the 

 time of development 

 of different parts of the 

 embryon, the openings 

 of the nostrils appear 

 in the second half of 

 the second month; a 

 little elevation, the nose, 

 appears between these 

 openings, and the nasal 

 cavity begins to be sepa- 

 rated from the mouth. 

 The lips are distinct 

 during the third month, 

 and the tongue first ap- 

 pears in the course of 

 the seventh week. 1 



The above sketch of 

 the mode of development of the face enables us to under- 

 stand the origin of certain of the more common malforma- 



1 BURDACH, Traite de physiologic, Paris, 1838, tome Hi., pp. 496, 498. 



Mouth of a human embryon of from twenty -five to 

 twenty-eight days ; magnified fifteen diameters. 

 1, median or frontal process, the inferior portion of 

 which is considerably enlarged ; 2, right nostril ; 3, 

 left nostril; 4, 4, inferior maxillary processes, al- 

 ready united in the median line; 5, 5, superior 

 maxillary processes, which have become quite 

 prominent and have descended to the level of the 

 slope of the frontal process ; 6, mouth ; 7, first vis- 

 ceral arch; 8, second visceral arch; 9, third vis- 

 ceral arch ; 10, eye ; 11, ear. (SAPPKY, Traite cPana- 

 tomie, Paris, 1874, tome iv., p. 72.) 



