Il8 PRIMATE ALVEOLINGUAL SALIVARY AREA 



thus bridging the intervals to form a continuous epithelial keel whose 

 canaHzation will establish the definite duct. 



This observation is of ver\' great significance because it establishes 

 the morphogenetic principle of ultimately continuous glandular ducts 

 by union of originally separate and distinct saHvary anlages. This 

 process is extremely reduced and evanescent in the mammahan embryo, 

 but its occurrence, even to the limited degree observed, establishes its 

 validity as a developmental character in earher phylogenetic conditions. 



4. The separate and distinct glands which, as the lesser sublingual 

 group, occupy the lateral alveoUngual district in all adult primates, 

 appear in the human embryo relatively late ontogenetically. The 

 elements which first develop sprout at intervals from a continuous 

 lateral epithelial keel of the alveoKngual area, the most cranial buds 

 appearing first. In the later stages these lose the early association 

 with the keel, while multiple additional elements (ChieN-itz, Hammar) 

 develop as direct individual derivatives from the epithehum of the 

 lesser subhngual field. 



It seems proper to interpret these ontogenetic findings in the follow- 

 ing sense in their bearing on the phylogenetic histor\- of the alveo- 

 lingual field : — 



a. The separate and individual glands forming the lateral lesser 

 sublingual group represent the more primitive archeal t}pe of glandu- 

 lar development of the oral floor. 



b. In the median districts of the submaxillary, and of the more in- 

 constant greater subhngual, they have ver>" largely abandoned this 

 primitive type by combining to form definite major glands with com- 

 mon ducts. The discontinuous development of the latter, by fusion 

 of originally separate anlages of the epithehal keel, is the last remi- 

 niscence of phylogenetically older conditions. 



c. The lateral group of the lesser sublingual glands, on the other 

 hand, ver>- largely maintains the primitive type of separate individual 

 glands each with its own short duct. 



d. The lateral anlages, which are the first to appear ontogenetically, 

 seem inclined to follow the phylogenetic advance which already com- 

 pletely dominates the submaxillary, and, to a lesser degree, the greater 

 sublingual hne. This is manifested by the fact that the earlier lesser 

 subungual elements are associated with an epithehal crest or keel. 



