352 MAMMALIAN ALVEOLINGUAL SALIVARY AREA 



Of the development of the caudal members of the lesser sublingual 

 series, which in some forms extend into continuity with the isthmian 

 glands, and of the elements which are placed mesal to the large ducts, 

 such as Weber's gland in man, we have at present no information. 

 Their morphologic status has been described elsewhere in this work 

 (Parts I and III). 



SUMMARY 



1. The gland complex of the alveolingual region, on both compara- 

 tive and developmental grounds, admits of division into sagittal com- 

 ponents, the submaxillary, the sublinguahs major, the sublinguales 

 minores. Primitively these are arranged in a horizontal plane, the 

 submaxillary mesal, the sublinguahs major intermediate, the sublin- 

 guales minores lateral ; in the course of development they become 

 oriented in a dorsoventral plane, retaining their reciprocal relations ; 

 the submaxillary becomes ventral, the sublinguahs major remains 

 intermediate, the orifices of the sublinguales minores become dorsal. 



2. A gland cannot be defined absolutely by the site of its orifice 

 nor is it yet certain that the point at which proUferation begins is an 

 absolute criterion. In view of the fact that gland development here 

 takes place in a shifting plate of epithehum, it is evident that the site 

 of an anlage in the transverse plane is the resultant of the rate of the 

 shift and the time at wliich prohferation is initiated. In determining 

 the status of a gland its whole developmental history must be borne in 

 mind. The topography of the adult is indicative mainly of the degree 

 of development of the element ; a higher degree of morphologic im- 

 portance attaches to the intrinsic relations of the ducts in the supramy- 

 lohyoid portion of their course. In view of the existence of mixed 

 glands, the general character of their secretory epithehum cannot 

 afford a criterion of their morphologic status. 



3. The submaxillary and subhnguahs major can be interpreted as 

 equivalent to plurahties of simple glands, rows of which have been 

 condensed to form the ducts. These elements manifest some inde- 

 pendence in the formation at times of outlying segments of the keels, 

 and at times of a late efflorescence of the ducts. This interpretation 

 affords an explanation of the otherwise perplexing ontogenetic appear- 

 ance of these mammaUan neomorphs, which long antedate their 



