DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 287 



element. The mesenchyme between the duct and the flange is somewhat 

 denser than elsewhere in the vicinity, an appearance in the case of the 

 parotid associated with the destruction of the intermediate element. 

 On the other hand, it is possible that at this stage the free duct is 

 formed as yet solely by the distal growth of the sprout, and the con- 

 cavity of the caudal border of the flange may possibly be due to the 

 traction of the sprout upon the flange ; the thickening in the mesen- 

 chyme may be antecedent to the development of a gap in the flange. 

 The caudal border retains this character while it remains posthngual 

 in position (embryos of 15-16 miUimeters). When the separation 

 has advanced farther along the sulcus and has reached the lingual 

 crossing, the type changes slightly (Fig. 142). There is still the dorsal 

 kink between the intermediate element and the postglandular flange. 

 But the whole flange having narrowed, these elements, especially the 

 intermediate, are much smaller. There is only a slight constriction 

 between the duct and the intermediate element, and the actual break 

 occurs between the intermediate element and the postglandular flange. 

 In this region, therefore, the intermediate element persists attached 

 to the duct and is not destroyed as farther caudad. The appearances 

 at this stage suggest strongly the condition of the parotid, in which an 

 orbitoparotid is situated at the angle where the duct joins the mouth. 

 This type is usual up to the stage of 20 millimeters. In a minority 

 of cases the break occurs at the dorsal border of the duct, and the in- 

 termediate element is left attached to the postglandular flange. The 

 intermediate element never, in the cat, gives rise to sprouts, nor does 

 it long remain visible. The duct soon loses its slightly hourglass shape, 

 becomes oval, and finally circular in section, and the intermediate 

 element is completely effaced. Its early disappearance and morpho- 

 genetic insignificance in the cat may account for the irregularities in 

 its behavior in the process of separation. Its presence has been re- 

 corded in the human embryo ; and in the adult primate, the dorsal 

 accessory submaxillary of Huntington is probably its derivative. 



A third type of separation characterizes embryos from 20 millimeters 

 to 35 millimeters in length. The attachment now is a simple keel, 

 constricted at its base in its caudal sections, wliile the duct is freed 

 simply by the deepening of the constriction; the intermediate ele- 

 ment is no longer present (Fig. 143). The anlage now extends far 



