DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 233 



evident that the intermediate portion of the flange has been reduced, 

 a concomitant thickening occurring in the mesenchyme, and that only 

 the thickened border of the flange gives rise to the parotid duct. The 

 retention of primitive conditions in the cranial sections of the aniage 

 gives ground to infer that meanwhile the fold continues to advance. 

 The proliferation of the duct advances very slowly along the margin 

 of the fold and has not yet reached its cranial extremity (Figs. 75-78). 



The character of the flange alters httle in succeeding stages, until 

 the embryo has attained a length of 20 millimeters. An example near 

 the upper limit of this period is shown in Figs. 82-87, '^ series of alter- 

 nate sections from the 19 millimeter embryo. No. 277. The flange has 

 a sagittal length of 54 /j-. Its bulk is somewhat greater, but in other 

 respects it closely resembles the anlages of earlier stages. In Fig. 83 

 there is a very slight thickening of the basal cells at the fundus of the 

 buccal sulcus. 



Thus far the liistory of the parotid may be summarized as, first, 

 the formation of a flange by the compression of an open fold, and 

 second, a process of proliferation along the free border of the fold 

 advancing towards the fundus of the buccal sulcus. The duct thus 

 formed is freed by the destruction of the intermediate portion of the 

 fold. This has now disappeared, and the proliferation is on the point 

 of extending craniad along the oral epithelium proper; coincidently 

 the aniage abandons its sulcal position. 



In the 20 millimeter embryo. No. 241 (Figs. 88-94) , the attachment of 

 the parotid is formed by a keel, 50 m in length, composed of cells re- 

 sembling the basal cells of the oral epithelium, deeply staining through- 

 out. It diminishes craniad so gradually that it is difficult to deter- 

 mine the precise point at which it stops. Caudad it is constricted at 

 its junction with the oral epithehum. Its attachment is fundal except 

 for its cranial extremity, which deviates dorsad from the fundus of 

 the buccal sulcus, which is here curving ventrad toward the angulus 

 oris. 



In the 21 niillinieter embryo, No. 242, the attachment is parietal in 

 its whole extent. It has a length of 67 /*. It is composed of basal cells 

 alone, staining deeply throughout and containing no a.xial line of 

 periderm. The stratum corneum, which is tloick in the fundus of the 

 buccal sulcus, does not enter the keel. In its caudal section it is slightly 



