238 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



thickening. and, subsequently deepening, forms a new border for the 

 vestibule ventrad of the parotid, merges farther craniad with the 

 fundus of the buccal sulcus. On account of the minute size of the 

 new element it seems more natural to regard the resulting furrow as 

 the representative of the buccal sulcus, which continues to lengthen 

 as formerly, by the advance of the angulus, there being no evidence 

 to show that in tlois region a secondary fundus is formed. 



The intermediate region, extending from the parotid flange to the 

 orbital angle, must be considered in more detail. 



Here the buccal sulcus becomes reduced and is finally obliterated. 

 The changes are, however, very gradual, and e.xtend over a long period 

 of development; the embryo of 51 millimeters is the first in which 

 actual interruption of the sulcus is found. 



The embryo of ig.5 milHmeters (Figs. 82-87), apart from increase 

 of size, has not advanced greatly beyond the stage attained by 

 the 15 millimeter embryos. The superior alveobuccal sulcus (25) is con- 

 fined to the immediate vicinity of the parotid. It can be recognized in 

 Figs. 84 and 85 ; in Fig. 86 it has completely disappeared. Craniad 

 of the parotid the buccal sulcus is very broad, and while presenting a 

 generally rounded outline, yet shows in the ectal contour of its epithe- 

 lium two faint angles, of which the dorsal is continuous with the 

 superior alveobuccal sulcus. The ventral soon becomes deep and is 

 continued to the angulus oris. The inferior alveobuccal sulcus is 

 broad and shallow ; towards the middle of its concavity the thickness 

 of its epithelium increases slightly. The vertical extent of the vesti- 

 bule has markedly increased and its roof and floor meet at a wider angle. 



In the 20 millimeter embryo (Figs. 88-94) the changes are clear and 

 definite. Dorsad of the parotid the angle of the superior alveobuccal 

 sulcus is chstinct. It is still confined to the region of the parotid and 

 is separated by a long interval from the secondary buccal sulcus. 

 The inferior alveobuccal sulcus is deeper and more angular at its 

 fundus, and in its lateral wall the sprouts of two rows of glands 

 have appeared. The superior and inferior alveolabial sulci have also 

 appeared. The former is represented by an angle in the epithehum 

 of the roof of the mouth at some distance laterad to the dental anlages. 

 It hes wholly craniad of the plane of the anguU oris, but otherwise 

 it closely resembles the superior alveobuccal sulcus at this stage. 



