DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 237 



lar process as a whole in comparison with the maxillary ;. for in the 

 roof of the mouth at this period the transverse increment is greatest 

 in the region of the palate process and the craniolingual plane, 

 while the increase of the maxillary process is small. In this embryo 

 the vertical extent of the vestibule is greatest in the plane of the parotid. 

 Caudad and craniad it lessens, and the roof and floor conform more 

 closely in relief. The changes which supervene and eventually trans- 

 form the vestibule from a nearly horizontal to a vertical cleft are 

 initiated in tliis intermediate region of the cavity, and thence extend 

 caudad and craniad without, however, affecting the terminal portions 

 of the buccal sulcus. The secondary buccal sulcus from the orbital 

 angle caudad escapes obliteration, as does also the cranial segment 

 in the vicinity of the postangular bend and the angulus oris. 



In the embryos of 15 milhmeters (Figs. 66-81) the buccal sulcus is 

 wide with a rounded fundus in the parotid region and immediately 

 craniad, gradually narrowing thence in both directions to a more acutely 

 angular furrow. Between the fundus and the superior dental ridge a 

 faint angle is observable, at which the inclination of the ventrally 

 sloping roof is slightly increased ; this is the superior alveobuccal 

 sulcus. In the floor the concavity of the inferior alveobuccal sulcus 

 has increased ; the thickening of its epithehum is, however, scarcely 

 perceptible. From the buccal sulcus mesad to the dental ridges the 

 cavity increases in height and , has now a < -shaped section. The 

 sagittal length of the region affected is as yet small. In embryo 

 No. 216 (Figs. 74-79) the furrow at the mesal border of the parotid 

 convexity is better marked. Caudad and craniad of the parotid 

 flange it merges with the buccal sulcus. With reference to this form- 

 ing furrow the parotid is already parietal ; the fundus of the buccal 

 sulcus having been utilized to form its flange, a new fundus is formed 

 to one side, as in the case of the orbital inclusion, with the difference 

 that it is here produced on the ventral aspect of the obstructing fold. 



A series of changes are thus initiated by which new sulci are sub- 

 stituted for the buccal sulcus in almost its whole length. Caudad the 

 process has been followed in detail in connection with the orbital 

 inclusion. The changes at the cranial end of the sulcus may here be 

 briefly dismissed. It has been said that the small furrow, which 

 appears first mesal to the parotid fold as the limit of its epithehal 



