62 THE DEVELOPMENT OF THE SALIVARY GLANDS IN MAN 



gradually the sulcus regains its lumen. But to its fundus are now 

 attached the keels of the submaxillary and greater subhngual glands. 

 The whole of the duct appears therefore to owe its formation to pro- 

 liferation locahzed at the fundus of the lingual sulcus, and proceeding 

 in a caudocranial direction ; only in its caudal portion the sulcus has 

 hrst been reduced to a flange, the free border of which represents its 

 primitive fundus. The flange, as such, does not directly give rise to 

 the duct, being lost in the process of its separation, but serves rather 

 to support the marginal prohferation and to determine the direction 

 of the growth of the sprout away from the alveolingual region. The 

 formation of the fold is explained by His as incident to the enlarge- 

 ment of the tongue, and the resistance offered its dorsal expansion by 

 the roof of the mouth. In this process the bulky submaxillary gang- 

 lion would seem from its situation to be also a factor. The view here 

 taken of the mode of formation of the submaxillary duct is supported 

 by the findings in the cat, where the lingual sulcus appears in two seg- 

 ments, which in a minority of cases fail to become continuous ; yet 

 over the gap the submaxillary advances by an epithelial keel, which is 

 precisely similar to those more usual ones where the sulcus is present. 

 Other glands in the cat, for example the orbitals, have ducts formed 

 later than their sprouts and prolonged along the oral epithelium in 

 the form of keels, without the intervention of any sulcus. The same is 

 true of the human greater sublingual in so far as it is attached to the 

 submaxillary, and probably also of the apical gland of the tongue. It 

 would appear therefore that while the relation of a gland to a sulcus 

 may in some way favor and accelerate the formation of its anlage, yet 

 the actual material for its duct is formed by the proliferation of new 

 cells and not the working over of materials that have once formed the 

 walls of the sulcus. 



The separation of the duct is accompanied by a solution of continuity 

 and probably also by a loss of substance in the flange. The 20 milli- 

 meter embryo affords evidence of its incomplete reduction, in the post- 

 glandular flange (ij) extending along the lingual sulcus caudad to the 

 submaxillary. The flange is constantly present in the cat, where it is 

 reduced caudocrainad, pari passu with the advance of the duct. In 

 this human embryo it presents evidence of constriction which may be 

 preliminary to its reduction, as in the 22 millimeter embryo it has en- 



