THE DEVELOPMENT OF THE SALIVARY GLANDS IN MAN 65 



of the walls of Chievitz's fissure ; there are, however, no data to de- 

 cide the point, and the j^rcfrenular position may be acquired merely by 

 unequal growth in the parts about the frenulum. 



The development of the lumen is preceded by changes in the central 

 cells of the duct, the cytoplasm of which stains faintly, while the nuclei 

 become pyknotic. The lumen in its first appearance is discontinuous 

 (Chievitz, 8 weeks), a condition retained on one side in the 22 milli- 

 meter embryo, where it is lined by a single layer of squamous cells, the 

 remainder of the wall being composed of two rows of polyhedral ele- 

 ments. In older embryos to the stage of 5 centimeters the duct epi- 

 thelium is composed of two rows of low columnar cells (Chievitz, 

 Bujard). 



The greater sublingual gland makes its appearance at 8 weeks as a 

 rounded process, attached to the lateral surface of the submaxillary 

 flange (Chievitz). In the 20 millimeter embryo it is represented by 

 a triangular keel resembling in form the early anlage of the subma.xil- 

 lary, but directed laterad and in the horizontal plane. At its free 

 angle the prohferation of a sprout has just begun. It is prolonged 

 craniad by a keel along the subma.villary flange and then independently 

 along the lingual sulcus. Its attachment is in line with the advancing 

 gap in the submaxillary flange (Fig. 26), which may pass either dorsal 

 or ventral to it, leaving it attached in the one case to the postglandular 

 flange, in the other to the submaxillary duct, as on the left and right 

 sides respectively of this embryo. In the older embryos, the greater 

 sublingual, when present, is attached to the submaxillary duct, so 

 that it would appear, in the Ught of our present knowledge, that the 

 solution of continuity in the flange of the latter is usually dorsal to the 

 attachment of the greater sublingual anlage. Here there can be no 

 question but that this advance of the duct is due to the proliferation, 

 and subsequent constriction of a crest, for in its inception, apparently, 

 the anlage is attached to the submaxillary flange and not to a sulcus. 

 In the 20 millimeter embryo it has acquired an independent keel along 

 the lingual sulcus, lateral to that of the submaxillary, while in embryos 

 of 22 millimeters and over it is attached to the pro.ximal portion of the 

 submaxillary duct. Here the union of the two crests is plainly secon- 

 dary, and not primary as appears to be the case with the caudal por- 

 tions of the anlages in man. It is easy to suppose that the two crests 



