PRIMATE ALVEOLINGUAL SALIVARY AREA II9 



If they had followed this first impulse toward a higher type of com- 

 pound glandular development the temporary keel would have evolved 

 into the common duct draining a group of lesser subhngual elements 

 now united within the frame of a separate major gland. The tendency 

 toward the formation of such a gland evidently exists in the lesser sub- 

 lingual field, but is, in the evolutionary sense, not yet sufficiently de- 

 veloped to produce typical and constant adult results. Chi the con- 

 trary, the attempt on the part of the first lesser sublingual elements 

 toward a definite association into a separate gland with common duct 

 is temporary and soon abandoned. The components implicated in 

 this attempt then revert to the common primitive type and are in- 

 cluded in the group of the more numerous buds which appear at a 

 later ontogenetic period and remain from the beginning as separate 

 individual structures. It is interesting to note that the more lughly 

 advanced and special components of the alveolingual complex, as the 

 submaxillary, predominant in the adult, are also the first and most 

 fixed to appear ontogenetically, whereas the phylogenetically more 

 ancient and primitive form, as the lesser sublingual group, develops 

 at a much later embryonic period. Further, that this chronologically 

 earlier and more advanced condition is manifested even within the 

 confines, of the more primitive lateral lesser sublingual area by those 

 components which, through association with a temporary epithelial 

 crest, aspire toward the assumption of the more highly differentiated 

 medial type of separate major gland development, even although 

 they do not ultimately attain this status. It suggests that the line 

 of greater structural and functional evolution has traveled meso- 

 laterad from the lingual to the alveolar border of a common primitive 

 uniform glandiferous intermandibular area. 



5. If the above suggested interpretation of the ontogenetic condi- 

 tions is correct, the primate alveohngual saUvary field illustrates two 

 important embryonic conditions : — 



a. In selective development, with the greater structural and func- 

 tional advance of individual districts of a common field, the anlages of 

 the portions so selected and differentiated appear earher in the ontog- 

 eny than the components of the more primitive areas. The potential 

 greater functional value of the preferred elements to the organism as 

 a whole may account for this preference. 



