DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 211 



of 60 fi. reckoned by sections. In section (Fig. 19) the fissure is 

 obliterated by approximation of its walls and a minute flange is formed, 

 the pale center of which is continuous with the remnant of the fissure 

 that indents its base. The pale area in the flange therefore represents 

 an obliterated portion of the fissure ; its pallor is due to the presence 

 of cells with faintly staining cytoplasm. Similar pale areas occur in 

 the flanges, ducts, and buds of all the salivary glands. In the case of 

 a flange they undoubtedly arc included periderm cells, which in this 

 9 millimeter embryo are present upon the surface of considerable 

 areas of the oral epithelium. In buds their presence must receive 

 another explanation. Here they are not flattened, but polygonal in 

 shape ; in their faintly staining clear cytoplasm, and in their pyknotic 

 nuclei they resemble periderm cells, and are probably the result of an 

 analogous cytomorphosis, possibly dependent on their distance from 

 the basement membrane and their, in consequence, less advantageous 

 nutrition. Their presence causes the centers of the salivary anlages 

 to appear pale, and with low magnification suggests a lumen long 

 before one is actually present. 



The embryos of 9.2 to 10.5 millimeters form a close series showing 

 the gradual advance of the fold from the mandibular crossing to the 

 angulus oris ; a process of constriction is begun by which the fold is 

 ultimately separated from the oral epithehum, and the fold itself is 

 differentiated into two areas, a caudal narrow, and a cranial broad 

 portion. Figure 21 is from a reconstruction of the ectal surface of 

 the epithelium of the marginal cavity in an embryo of 10 millimeters. 

 The orbital fold involves the greater part of the buccal sulcus. 

 The constriction is indicated by a small furrow on the dorsal surface 

 of the epithelium parallel to the buccal sulcus. This is shown in the 

 section (Fig. 20), where also a very faint ventral furrow can be dis- 

 tinguished. These furrows gradually deepen until they meet and free 

 the orbital inclusion. As they must frequently be referred to, they 

 v{\\\htiermeAi\i& separating sulci; it is seen that the dorsal slightly 

 precedes the ventral in development, being present indeed in the 

 9 millimeter embryo. In the model only the constricted portion of 

 the fold can be seen. Tliis forms a solid cyUnder of uniform diameter 

 and circular cros.s-seclion, the pars cylindrica of the orbital inclusion. 

 Further craniad the fold loses its external relief, while in the sections 



