278 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



12. j millimeter embryo. No. 264. — The flange is lingual and post- 

 lingual in position. It retains its wavelike form, coming gradually to 

 a maximum and then declining. It is also concave laterad. In these 

 features it closely resembles the anlage of the 12 millimeter embryo. 

 It is, however, of greater depth and more thickened at the border in its 

 sections of greatest breadth. This is the beginning of active prolif- 

 eration, which from its site is referable to the minute keel that ante- 

 dated the flange, and was carried ventrad in its formation as its free 

 border. 



7 J. 5 mUlimeter embryo, No. i8g {Figs. 36- j8). — In these sections 

 is shown the topography of the alveolingual region. The intermedi- 

 ate region of the sulcus is angular, its epithelium tliickened to a slight 

 keel at the fundus (Fig. 36). Caudad the sulcus is reduced to a flange 

 wliich has a considerable depth at the lingual crossing (Fig. 38). Here 

 the bulky submaxillary ganglion lies lateral to the flange, and the nerve 

 carrying an extension of its gangUon, sweeps in an arch ventrad of 

 the anlage to reach the tongue. Caudad of the nerve the anlage shows 

 a great increase in size, its enlarged fundus being directed ventrad and 

 slightly laterad, toward a moderately well circumscribed area of dense 

 mesenchyme (Fig. 39). Ventrad of the alveolingual region is a sagittal 

 tract of mesenchyme, limited laterad by Meckel's cartilage, mesad by 

 the genioglossus, and ventrad by the mylohyoid muscle (Fig. 37). 

 These, save the cartilage, which is inclosed in. the ossification of the 

 mandible, are permanent relations and narrowly confine the space 

 available for glandular development. Caudad, beyond the border of 

 the mylohyoid, this supramylohyoid mesenchyme becomes continu- 

 ous with the dense area just mentioned, through the broad interval 

 between the hypoglossal nerve and Meckel's cartilage (Fig. 39). 

 The lingual nerve and its ganglion are near the caudal border of the 

 mylohyoid, and the proliferation center of the submaxillary, just 

 caudal to the lingua! crossing, is close to the junction of the two areas 

 of mesench>-me. Its subsequent growth takes place in both direc- 

 tions, distad into the mesenchymal condensation, and proximad along 

 the prelingual segment of the Ungual sulcus. 



In the section of greatest breadth (Fig. 39) three regions can be 

 recognized in the anlage, defined by very slight constrictions ; ventrad 

 is the enlargement of the sprout ; dorsad a portion of the flange at- 



