286 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



The duct formed by proliferation in the border of the flange and con- 

 tinued craniad by proHferation in the lateral wall of the hngual sulcus, 

 is freed by a process of constriction, advancing craniad from the caudal 

 border of the flange. This is begun in some of the 13.5 millimeter 

 embryos. Just caudad of the hngual nerve, the solid duct is 

 free (Fig. 136). Here there persists along the lingual sulcus a rem- 

 nant of the flange, the postglandular flange {31). This represents the 

 caudal portion of the primitive flange, wliich escapes destruction in the 

 freeing of the duct. It is precisely analogous to the inconstant post- 

 parotid flange, but unlike that element is never in any of our embryos 

 the source of a sprout. It is constant in embryos of 20 millimeters 

 and under. In embryos of 18 millimeters and less it extends from the 

 angle of junction of the duct and hngual sulcus caudad to the hngual 

 crossing. In older embryos it is rapidly reduced in a caudocranial 

 direction, and in those of more than 20 milhmeters it is altogether ab- 

 sent. With it disappears, also, the hngual sulcus, and the alveolingual 

 region passes without demarcation by an even curve into the side of 

 the tongue (Figs. 144, 146). The caudal segment of the sulcus then 

 seems to form only in the interests of the submaxillary, and as soon as 

 the duct has made its advance hastens to disappear. 



The sections at the lingual level in embryos of 13.5-15 milhmeters 

 (Fig. 141) throw some Ught upon the nature of the constriction. 

 Here the flange projects ventrolaterad from the sidcus and enters 

 into close relations with the hngual nerve. The flange is twice kinked 

 and shghtly bent at the kinks as though pressed upon by the nerve. 

 Three areas are distinguishable, a dorsal one continuous caudad with 

 the postglandular flange (j/), a ventral one continuous with the free- 

 growing sprout (jo) , and an intermediate element {30a) which behaves 

 differently at different periods. In embryos of 13. 5-15 milhmeters, 

 when separation is initiated, the flange of the submaxillary has a 

 triangular contour (Fig. 139) with a concave caudal border. The in- 

 termediate portion of the flange corresponds to the crown of this 

 curve. In sections passing through the anlage close to the border 

 the flange has the appearance shown in Fig. 136. In immediately suc- 

 ceeding sections the postglandular flange, adhering to the sulcus, is 

 separated by a considerable gap from the free duct, wliich lies almost 

 vertically below it. In many cases there is no sign of an intermediate 



