276 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



As we are here about to follow a development remarkably fixed in 

 tjqae, and subject only to slight variations in its rate as a whole, and to 

 an equally small degree in the relative rates of its component processes, 

 it will be convenient simply to report the findings in individual em- 

 bryos, which are taken as representative of average conditions for 

 their several lengths. In each the right side is described. 



// millimeter embryo. No. 21 j (Figs. 11S-121). — The tongue at its 

 tip is triangular in section and continued as a diminishing ridge in 

 the gutter between the ends of the mandibular processes. At its sides 

 it is defined by shallow concavities which, near the tip and in the region 

 of the Ungual nerve, become angular, and form distinct boundaries 

 between the tongue and the alveolingual regions. Near the lingual 

 crossing the angle becomes more acute (Fig. 120), and caudad shows a 

 minute vertical keel of epithelium (Fig. 121) which seems to be a 

 remnant of the primitive thickening, which extends from the buccal 

 sulcus to the lateral tongue swelling. It is to be noted that we are 

 deahng with a very early condition of the sulcus before it has advanced 

 beyond the condition of an angle in any considerable portion of its 

 course, and that the keel referred to antedates the appearance of the 

 actual sulcus. 



ii.j millimeter embryo. No. 2j6 (Figs. 2j-jo). — The sulcus presents 

 cranial, intermediate, and caudal segments, the latter two alone being 

 shown in these figures. The cranial segment has become very deep; 

 it is directed mesad and ventrad, undermining the tongue, to a 

 degree which increases craniad, until eventually it meets its fellow of 

 the opposite side, and the tip of the tongue is thus freed from the floor 

 of the mouth for a short distance. As the sulci of the two sides deepen, 

 they also become broader, and near this confluence the tongue is con- 

 nected to the floor of the mouth only by a narrow strip of mesench}Tne 

 which intervenes between the broad fundi of the sulci. The cranial 

 border of this fold is vertical, and in the section in which the sulci 

 unite, disappears in its whole extent. At this stage, therefore, the 

 cranial border of the frenidum or plica mediana corresponds with the 

 confluence of the sulci. This relation is maintained to the stage seen 

 in the 17 millimeter embr^'o, after which new conditions are cstab- 

 Hshed. The intermediate segment of the sulcus is angular, becoming 

 more acute as the region of the lingual nerve is approached (Figs. 



