DEVELOPMENT OF THE ALIMENTARY TUBE AND APPENDED ORGANS. 297 



The main portion of the gland is produced by a sprouting of the epithelium 

 from the angle of union of the two free borders of the flange and grows deep 

 into the mesenchyme along the mesial side of the ramus of the mandible. 

 The sprouts branch repeatedly in the course of their development, thus laying 

 the foundation for the division of the gland into lobes and lobules. 



The distal end of the duct of the submaxillary (Wharton's) is formed from 

 the ridge-like thickening of the free margin of the flange through a dissolu- 

 tion of the greater part of the flange between the lingual sulcus and the 

 thickened margin itself, thus freeing this portion of the duct from the sulcus. 

 By a continuation of the growth which produced the ridge along the free 

 border of the original flange an extension of this same ridge is produced along 

 the bottom of the lingual sulcus forward toward the chin region. This portion 

 of the ridge is progressively constricted off from the sulcus from cehind 

 forward, until finally the attachment of the duct reaches its definitive position 

 at the side of the frenulum linguae. 



The anlage of the Bartolinian element of the suUingual gland appears as 

 a smaller flange attached to the lateral border of the submaxillary flange near 

 the crossing of the lingual nerve and prolonged forward by an interrupted 

 crest along the lingual sulcus. Its later development is similar to that of the 

 submaxillary. 



A small medial flange also on the submaxillary flange gives rise to a sprout 

 in much the same manner as the other anlagen. While the history of this 

 anlage is not complete in the human embryo, it probably gives rise to the 

 anterior lingual gland (gland of Bland in and Nuhn). The alveolingual ele- 

 ments arise from a keel attached to the alveolingual sulcus (the groove 

 between the floor of the mouth and the alveolar process of the lower jaw). 



The parotid gland originates from the buccal sulcus in essentially the same 

 way as the submaxillary arises from the lingual sulcus. The anlage then 

 continues to grow through the mesenchyme of the cheek across the masseter 

 muscle, the distal end branching freely to form the secreting portion of the 

 gland. The outgrowths are at first solid, but later become hollow, the 

 proximal portion of the original outgrowth forming the parotid (Steno's) 

 duct, the more distal portions forming the smaller ducts and terminal tvbales. 



The histogenetic changes in the salivary glands probably continue until the 

 child takes solid food, when the glands become of greater functional importance. 

 In the parotid gland, which is serous in man, the original, undifferentiated 

 epithelial cells undergo changes in form and arrangement so that by the 

 twenty-second week the larger ducts are lined with a two-layered epithelium, 

 the smaller ducts with a simple cuboidal epithelium, and the terminal tubules with 

 a single layer of high columnar cells. The two-layered epithelium in the larger 

 ducts persists. The ducts lined with the cuboidal epithelium become the 



