294 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



In embryos of i8 millimeters* the greater sublingual begins to 

 advance, forms a free-growing sprout, and separates a portion of its 

 duct from the alveolingual epithelium by the continuance of the con- 

 striction already initiated at its caudal extremity. 



The advance takes place along a line converging slightly towards 

 the lingual sulcus, but never joining the keel of the submaxillary. 

 The cranial extremity retains the character of a gradual subsidence 

 into a more diffuse thickening. In embryos of 19-20 miUimeters 

 the termination is more abrupt, the thickening less marked. With 

 regard to the latter, it will be remembered that primitively it covers 

 the whole alveolingual region, and yet at the time just prior to the 

 establishment of the greater sublingual, it has become confined to the 

 portion of the gutter caudal to the Ungual crossing. In succeeding 

 stages it reappears in a Hmited area in advance of the keel of the anlage 

 with which it merges. A similar sequence of events characterizes, 

 also, the advance of the submaxillary, but here the thickening is a 

 sharply circumscribed, almost Unear keel. Both glands appear in re- 

 gions where the diminishing thickening has not wholly disappeared, 

 and form their anlages out of its remains, the submaxillary partially, 

 the greater subUngual wholly. The advance of both glands proceeds 

 over an area from which the thickening has vanished, but as they 

 advance a localized area of the epithelium recovers its powers of 

 relatively rapid proliferation and supplies the material for the ducts. 

 The more diffuse condition of this element in the hne of the greater 

 subungual may indicate a less degree of fixity in its line, or may have 

 reference to the late elflorescence of its duct (Figs. 109, 114). 



The interpretation of this anlage as a keel and not a flange is 

 strengthened by its mode of separation. Almost from the first 

 a constriction is present in its caudal sections close to its attachment 

 to the oral epitheUum, which, deepening, cuts off the entire keel. No 

 portion of it is left adherent to the epitheUum, and there is no inter- 

 mediate portion destroyed in the process. Throughout, its separation 

 resembles the late stages of the parotid and submaxillary glands, and 

 on a larger scale the process of duct formation of the three cranial 

 orbitals. With them it constitutes a class intermediate between sulcal 



* The 16.5 millimeter embryo of Fig. 140 agrees in the development of the greater 

 sublingual with the i8 millimeter embryos. 



