DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 251 



larly undergoing a diminution of length caudad proportional to the 

 length of the cranial process. This boundary is, therefore, subject 

 to fluctuating variation. Craniad, on the other hand, the interval 

 gains to the degree that the parotid advances, its flange being de- 

 stroyed in the process of freeing the duct. In cases where the reduction 

 of the fold is not total, a remnant maybe left attached to the buccal 

 sulcus, in a position analogous to the postglandular flange of the sub- 

 maxillary. This eventually disappears, but first may serve as a start- 

 ing point of an orbitoparotid sprout. 



Caudad the interval is limited by the cranial process of the orbital 

 inclusion, until its separation from the oral epithehum takes place. 

 This occurs in embryos ranging from 15 to 19.5 millimeters in length. 

 During the period of its attachment the fold continues to advance, so 

 that the length of the cranial process varies with the time of its sepa- 

 ration. An attempt was made to determine the cranial limit of the 

 orbital fold in embryos between 16.5 and 21 millimeters. For this 

 purpose the only available and not wholly satisfactory landmark is 

 the deep facial vein. This is, relative to the region in question, a large 

 structure, and has the further disadvantage of undergoing a shift 

 caudad during development, but this is very slight in degree during 

 the period here in question. The difficulty of its size may to some 

 extent be overcome by dividing its total width at the level of the sulcus 

 into halves. Four positions of the tip of the orbital inclusion may be 

 distinguished with reference to the vein, prevenous, venous I, II, 

 corresponding to the cranial and caudal halves of the vein, and post- 

 venous. The attached and free processes are tabulated separately. 



Table I 



