THE DEVELOPMENT OF THE SALIVARY GLANDS IN MAN 37 



presents itself as a slight projection from the ectal surface of the 

 epithelium, its cells having the same staining properties as the basal 

 cells. The periderm in these sections presents no disturbance of its 

 curve in the buccal sulcus, and there is no suggestion of a fissure or 

 fold to account for the crest, which in these sections appears to be no 

 more than a localized thickening of the oral epithelium. In the next 

 sections, however (Figs. lo, ii), and especially in the second, the crest 

 presents a pale center, which, with higher magnification, is found to 

 comprise an area of cells in which the cytoplasm stains little, while the 

 nuclei are pyknotic. Similar areas are noted in succeeding sections 

 at the attachment of the pedicle and have been already described in 

 the center of the parotid anlage. These cells placed far from the 

 basement membrane appear to undergo a cytomorphosis analogous 

 to that of the periderm cells of the oral cavity. As similar pale centers 

 appear in the secondary and tertiary sprouts of the submaxillary, they 

 need not be directly referred to the obliteration of the lumen of a 

 hypothetical fold, in which periderm had appeared before the lumen 

 was lost, but can as well be explained as preparatory to the acquisition 

 of a lumen in a solid epithelial plug. It is further to be noted that 

 these pale areas are separated from the periderm lining of the buccal 

 sulcus by deeply staining cells (Fig. ii), which would hardly be the 

 case were they extensions of that layer in a bUnd fold. The appear- 

 ances of the left side are similar, with the pale areas well marked. The 

 evidence here given seems to point to an interpretation of the pro- 

 parotid crest as a proliferation keel, an extension forward of the pro- 

 liferation of the parotid sprout so that one continuous process appears 

 in the formation of the duct as well as of the gland. This point will 

 be again referred to in the consideration of the submaxillary and 

 sublingual glands, where it appears that an essentially similar process 

 is at work. 



The foregoing is not intended to deny the existence of a parotid 

 fold, but greatly to hmit its role in the development of the gland. In 

 the cat a minute fold is formed, in connection with which the parotid 

 sprout makes its appearance. The subsequent history of the parotid 

 is the history of the sprout, from which the duct and the branches 

 of the gland are derived by proliferation. While I am not convinced 

 that such a fold of inception has as yet been observed in man, the 



