PRIMATE ALVEOLINGUAL SALIVARY AREA 121 



developed to the phyldgenetic point of yielding constant results, is 

 shown by the inconstant and variable occurrence of the greater sub- 

 lingual gland in the different primate genera and by the human adult 

 variants. When present, it is normally situated on the mesal aspect 

 of the remainder of the lesser sublingual mass of separate glands, 

 reducing over the area of its own extent, the bulk of the latter. In 

 only a single individual of all the primates examined (the variant speci- 

 men of Troglodytes shown in Fig. 2 of Part III) does it lie lateral to 

 the lesser sublingual group. Normally, therefore, it is intermediate 

 in position between the submaxillary and the lesser sublingual dis- 

 tricts. If, as above suggested, the evolutionary tendency toward the 

 production of major and functionally more effective glands manifests 

 itself in a mesolateral direction from the Ungual toward the alveolar 

 sulcus, the medial elements of the lesser subhngual group would be the 

 first to respond to this impulse, which may have attained the point of 

 establishing in a large nuniber of primates the intermediate greater 

 sublingual gland and duct. In this case the evanescent appearance 

 in rudiment of the same process in the remaining lesser subhngual 

 field may portend the gradual future acquisition of a distinct tliird 

 sublingual gland out of primitive component elements at present still 

 included in the general mass of the lesser sublingual group. 



7. While Schulte's researches clearly prove that mammalian inter- 

 mandibular sahvary development in general proceeds along typical 

 and definite hues, selected from the entire available alveohngual 

 field and separated from each other by barren and non-productive 

 intervals, yet he notes the occurrence, in these intervals, during the 

 ontogeny, of occasional rudimentary glandular anlages which do not 

 develop into permanent functional sahvary components. This ob- 

 servation others strong presumptive evidence in favor of the concept 

 of a primitive and uniform glandiferous oral floor, which potentially, 

 by phylogenetic selection, becomes subdivided into specialized and 

 independent districts. These ontogenetic observations, in themselves 

 scanty, are confirmed by the adult conditions in man and the lower 

 primates already recorded, such as the extension of individual elements 

 of the lesser sublingual type mesad of the line of the submaxillary duct. 



8. Lastly, liis anah'sis of the ontogenetic stages in this mammalian 

 salivary area proves the influence which the mechanical conditions 



