TOOTH DEVELOPMENT — DASYPUS NOVEMCINCTUS 675 



liiim but connection is again established in the fourth section. 

 In cross section this bud is nearly round; its peripheral cells are 

 columnar and are like those of the Malpighian layer of the oral 

 epithelium while the central cells resemble those of the stratum 

 corneum. Four sections posterior to the one shown in text fig- 

 ure 15, c is a conspicuous upgrowth of the oral epithelium (text 

 fig. 15, g) and in the fifth section (15 h) is an entirely detached 

 epithelial bud which continues through several sections (text 

 fig. 15, h, i, and j). The structure of these buds is shown in 

 figures 15 and 16. In this vicinity are a few remains of the den- 

 tal lamina but these have no connection with the epithelial 

 buds. 



In the same region of the premaxilla of a 65 mm. embryo there 

 occur four epithelial buds similar to those described above. 

 Two of these buds are still attached to the oral epithelium. 

 Figure 15 shows one of these attached buds, and figure 16 shows 

 a bud after it has become detached. Anterior to the first of these 

 buds is an upgrowth of the oral epithelium which is evidently 

 destined to give rise to a fifth bud. 



Figure 17 shows the structure of one of these buds or cysts in 

 an 82 mm. embryo. The cysts are larger than in preceding 

 stages. The periphery still resembles the Malpighian layer of 

 the oral epithelium, while the inside has a structure like that of 

 the stratum corneum The cells of the central portions are 

 becoming vesicular. The nuclei are irregular and show signs 

 of degeneration, and the cell walls are thickened as though being 

 transformed into horny material. This appearance is likewise 

 presented by the stratum corneum of the oral epithelium. 



In older embryos, the outside layer of the oral epithelium is 

 composed of a clear horny stratum which has arisen through the 

 cornification of the peripheral cells of the stratum corneum. If, 

 instead of being allowed to lie in a stright line, a strip of this oral 

 epithelium had been rolled up until the two ends met, the ap- 

 pearance would be similar to that of the epithelial cysts found 

 in these later stages. The peripheral layer takes the same 

 stain as the Malpighian layer of the oral epitheliimi. The cells 

 of this peripheral layer become much flattened, and at birth 



