206 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



to the lengthening of the buccal sulcus, whether at the angulus also 

 there may not be a progressive fusion. If so, the advance of the 

 angulus produces the buccal sulcus as a moving point describes a curve ; 

 if on the contrary no fusion occurs, then the angulus must be looked 

 upon as a definitive structure, bodily displaced craniad by growth 

 in the mesenchyme caudal to it. 



A striking feature of the development of the orbital inclusion and 

 of the parotid is the caudal displacement which these structures 

 undergo relative to the angulus oris (Figs. 34, 41, 45). The interval 

 between the angulus oris and the orbital inclusion, after a preliminary 

 stage to be discussed hereafter, steadily increases. The same holds 

 true of the parotid in the cat throughout its development. Tliis, of 

 course, must be explained by a more rapid growth of the interval. 

 But when we consider that the orbital inclusion practically reaches 

 the angulus in the 11.5 miUimeter embryos, and the parotid at 

 12 miUimeters is within a fewmicra of it at the preangular bend, we have 

 reduced the elongating interval practically to a growing point, the 

 angulus oris. 



Again in embryos between 8.5 millimeters and 10 millimeters in 

 length the marginal cavity and the postangular sulcus are horizontal 

 (Fig. 5). If in these embryos preangular sections are exaniined, the 

 maxillomandibular plane is found to be inclined ventrolaterad (Fig. 4). 

 Here the palate process has almost disappeared and the ma.xillary 

 has begun to overlap the mandibular process laterad. Farther 

 craniad the overlapping is even more marked. This condition is 

 retained in the adult as a wide, hairless area of the lower lip, which is 

 covered by the upper when the mouth is tightly shut. Could we 

 imagine the angulus to advance along the cleft between the maxillary 

 and mandibular processes keeping close to the surface, in later stages 

 the maxillomandibular plane at the angulus would not be horizontal 

 but ventrolaterally inclined. This condition is achieved at 11. 5 

 millimeters (Fig. 12) and marked at 12.5 millimeters (Fig. 15). 



In these and older embryos the overlapping of the mandible by the 

 maxillary process increases craniad, and usually attains such a degree 

 that towards the tip the mandible is covered comjiletely and concealed 

 from lateral view. From the side the cleft between the processes 

 appears to curve ventrad from the angulus. The angulus advancing 



