68 THE DEVELOPMENT OF THE SALIVARY GLANDS LN MAN 



its attachment and is continuous distad with the alveolar sulcus, the 

 cranial segment of which it seems to replace. The glands sprout from 

 this crest at intervals, the most cranial being first established. At a 

 later period they lose their association with the crest, and additional 

 ones are formed diffusely from the epithelium of the plica subUnguaUs 

 and the floor of the alveohngual gutter (Chievitz, Hammar, Bujard). 

 These glands then appear rather as diffuse products of the alveolingual 

 gutter, than as pecuhar derivatives of the alveolar sulcus which forms 

 its lateral limit. The early appearance of some of the glands in asso- 

 ciation with a crest and furrow merely indicates that in some way a 

 sulcal position favors the development of glands, and that those ele- 

 ments of the series which abut upon the furrow are accelerated and 

 antedate their fellows. The late appearance in ontogeny of these 

 simple and phylogeneticall}' ancient elements is noteworthy. 



In the embryo of 20 millimeters between the intermediate sulcus 

 and the lingual sulcus are a few small thickenings of the epithelium 

 which have disappeared in the embryo of 22 millimeters. These hke 

 the lesser subhngual glands seem referable to very primitive condi- 

 tions. If the diffuse glandular formation obtaining in this region in 

 some amphibians and in some reptiles be had in mind, these simple 

 glands of the mammal will appear as their direct equivalents, while 

 the larger elements may be interpreted as hypertrophied individuals 

 of the same series (Reichel),or, in view of the interruptions observed 

 in their formative crests, it may be preferable to regard them as rows 

 of primitively distinct elements condensed and fused to form the ducts, 

 while their individual tendencies to proHferate are retarded. That 

 they may at times become active in this direction is shown by the late 

 incrustation of some of the ducts with small lobules, for example, the 

 greater sublingual in the cat. At the mesal border of the primitive 

 gland field, perhaps in consequence of the presence of the lingual sul- 

 cus, the process of condensation attains its maximmn, and the line of 

 the submaxillary- is established. In the cat, at least, a second line is 

 established lateral to this, which in direction corresponds to the in- 

 termediate sulcus of man ; from it is derived the greater sublingual 

 gland. With the estabhshment of these dominant lines the inter- 

 vening area appears exhausted and produces no glands (cat) or merely 

 abortive rudiments (man). 



