DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 291 



shortened in the later stages. Here we may note that the length of 

 the keel in no wise expresses the activity of the prohferation, for these 

 short keels are advancing absolutely more rapidly than the long ones 

 of earlier embryos. In the light of these conditions the extremely 

 small epithelial plates at the angulus oris cannot be used as evidences 

 of a small degree of fusion between the maxillary and mandibular pro- 

 cesses. They indicate rather approximately equal rates in the process 

 of fusion and in that of reduction of the epithelium. 



In the 20 millimeter embryos the attachment of the submaxillary 

 keel was to the lateral wall of the lingual sulcus, a short distance from 

 its fundus. This parietal position it maintains, but the distance 

 between the fundus and the attachment increases, in part owing to 

 a deepening of the sulcus, in part to growth in breadth of the whole 

 region. 



Lateral to the Ungual sulcus the floor of the mouth becomes convex; 

 the convexity has a lateral limit in the circumflex sulcus which appears 

 concomitantly. The elevation is the plica subhngualis. In the 

 20 millimeter embryos it is slight in degree and limited to the frenular 

 region. Later it extends caudad and in the embryo of 70 millimeters 

 almost reaches the Ungual crossing. The still later reduction of the 

 caudal portion of the fold and its undermining by the sulcus, does not 

 fall witliin the period covered by the embryos of our series. In the 

 adult it is reduced to little more than a papilla, on which the ducts of 

 the submaxillary and greater sublingual open, situated close to the 

 symphysis, and attached to the plica mediana, traction upon which 

 will elevate it sufficiently to show that it is free of the floor of 

 the mouth. 



The attachment of the duct to the lateral wall of the lingual sulcus 

 causes it to be situated upon the pHca as soon as the latter appears. 

 Gradually it is carried craniad and gains an orifice near the cranial 

 end of the plica. At first located on its mesal surface, in the 51 milli- 

 meter embryo it has reached the summit of the convexity. 



The distal growth of the submaxillary is exceedingly vigorous. 

 Its bud is a large, solid, retort-shaped object from the first. In the 

 14 millimeter embryos its extremity is at the border of the mylo- 

 hyoid ; in the more advanced embryos of 15 millimeters it has reached 

 the center of its mesenchymal area. In the 16-16. 5 millimeter embryos 



