DEVELOPMENT OF THE DIGESTIVE TUBE 



609 



in the human embryo is formed, the external margins or primitive jaw area of 

 the oral cavity soon become differentiated into three general areas (fig. 288A) : 



( 1 ) an external marginal elevation, the rudiment of the labium or lip, 



(2) slightly mesial to the lip rudiment, a depressed area, the labial or 

 labiogingival groove, and 



(3) internal to this epithelial ingrowth, the gingiva or gum elevation. 



The latter overlies the developing jaw. From the mesial aspect of the labial 

 groove, an epithelial thickening forms which pushes inward into the tissue of 

 the gum or gingiva. This thickened ridge of epithelium forms the dental 

 lamina (ledge). (See fig. 288B, C.) 



After the dental ledge is formed, epithelial buds arise at intervals along the 

 ledge. These epithelial buds form the rudiments of the enamel organs. Each 

 enamel organ pushes downward into the mesenchyme of the gum and even- 

 tually forms a cup-shaped group of cells, enclosing a mass of mesenchyme, 



ARYTENOID SWELLINGS 



FORAMEN CECUM / 



YNGO- EPIGLOTTICA 

 SO -EPIGLOTTIC 



FOLD 



LATINE rONSlL 

 FORAMEN CECUM 

 LINGUAL TONSIL 



EPIGLOTTIS \ 



LARYNGEAL OPENING 



ARYEPIGLOTTIC FOLD 



ADITUS LARYNGIS 

 NTERARYTENOID NOTCH 

 ESOPHAGUS 



Fig. 285. Development of the tongue in the human embryo. (A-D drawn and modified 

 from Ziegler models. (A) Fourth week. (B) About fifth week. (C) 6th to 7th week; 

 IC mm. (D) 7th week; 14 mm. (E) Adult condition. Observe that the mandibular 

 lingual swellings give origin to the body of the tongue, while the copula forms the root 

 of the tongue. 



