PRIMATE ALVEOLINGUAL SALIVARY AREA 117 



3. The collection and interpretation of all available ontogenetic 

 data in support and definition of this theoretical morphogenetic field 

 and of its specialized lines of higher development. 



In pursuing this plan for determining the mutual relations of adult 

 salivary components of the sub- and inter-mandibular regions in 

 primates, and, secondarily, in other mammalian orders, it is desirable 

 at the very outset to assemble briefly the facts offered by mammalian 

 salivary ontogenesis in this region in support of the far more extensive 

 theoretical assumptions upon wliich the generalized interpretation 

 is based. Schulte's investigations of the development of the salivary 

 glands in the human embryo and in other mammals, notabl}' the cat 

 and pig, are given in full in other parts of this work (Parts II, VI, 

 VIII). 



For the purposes of the present consideration it is only necessary to 

 briefly define some of his results bearing directly upon the problems 

 here involved. 



He has established the following facts : — 



1. The primary anlage of a future gland or of a circumscribed 

 glandular area develops in a definite and constant situation and grows 

 thence in both directions, cephalad and caudad, by further extension 

 and proliferation of the glandular epithelium. 



2. In the components wliich appear in the adult as larger definite 

 glands with main ducts (submaxillary and greater sublingual) the 

 caudal extension is a continuous and uninterrupted ontogenetic process, 

 and unfolds, by epithehal proliferation, the secreting elements of the 

 gland proper, and the intraglandular system of ducts. The cephalic 

 extension, from the site of the primary embryonic anlage, forms the 

 extraglandular duct of the gland along the line of a primitive epithe- 

 hal keel, which subsequently becomes canalized. 



3. This cephalic prolongation of the glandular anlage may appear 

 as the continuous and uninterrupted development of the epithelial 

 keel. On the other hand the process may be discontinuous. In the 

 latter case the sagittal fine subsequently occupied by the completed 

 canal presents in the earlier stages segments of the epithelial keel 

 separated by barren intervals in which as yet no anlages of the future 

 duct exist. The latter is finally laid down by elongation of the primi- 

 tive separate anlages and their subsequent fusion with each other, 



