244 DE\'ELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



ation: first, the assumption by the anlage of a parietal position and, 

 second, the direction of its keel of proliferation. 



In the 15 millimeter embryo (Figs 75-78) the parotid still retains 

 in its flange a remnant of the buccal sulcus in the form of a minute 

 fissure. Ventral to the flange there is a minute bulging of the oral 

 epithelium. This increases slowly and, deepening laterad in the 

 embryo of 20 millimeters (Figs. 89-93), has come to form the lateral 

 border of the marginal cavity. Attention has already been called to 

 the similarity of the process to that at work in the displacement of the 

 orbital inclusion. The formation of the new fundus is the result of 

 unequal growth in the walls of the sulcus, and as a consequence fundal 

 structures are displaced to a parietal position. For convenience we 

 may term the new sulcus subparotid. In the 20 milhmeter embryo 

 it has deepened to such a degree, that the parotid attachment has 

 come to he midway between it and the superior alveobuccal furrow, 

 a position retained in the 25 millimeter embryo, while in those of 28 

 and 31 millimeters, it is nearer the last-named sulcus. The displace- 

 ment, which is dorsomesal along the sloping roof of the maxillo- 

 mandibular plane, becomes dorsal when the vertical cheek is formed. 



That the advance of the keel of the parotid along the oral epithelium 

 assists the dorsal displacement of its orifice is highly probable. The 

 proHferation keel extends craniad in line with the border of its flange. 

 This Une intersects that of the buccal sulcus at an acute angle, so 

 that its production craniad diverges from the ventrally curving 

 sulcus. As the parotid advances, therefore, it deviates from the sul- 

 cus dorsomesad. The degree of shifting attributable to this factor 

 appears to be extremely small. 



In the 25 milHmeter embryo the region of the parotid attachment 

 is slightly convex towards the oral cavity. In the embryo of 30 milli- 

 meters the convexity has increased and lengthened to form a sagittal 

 ridge limited dorsad by the superior alveobuccal sulcus, and ventrad 

 by the subparotid sulcus, a mere angle here in the caudal portion of 

 its extent. In the 51 miflimeter embryo the ridge extends from the 

 parotid orifice to the region of the orbital angle. Upon it open, in 

 addition to the parotid, the ducts of the three orbital glands, from 

 which circumstance it may be termed the stomal ridge. The sub- 

 parotid sulcus is still a mere angle, and has ceased to be continuous 



