DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 277 



23-25). Immediately in front of the nerve a minute crest appears 

 at the fundus (Figs. '26-2 7) which is solid and deeply staining. At 

 the Ungual crossing (Fig. 28) this has increased in height, but retains 

 the ventromedian inchnations of preceding sections. Caudad it is 

 larger, convex mesad, but with a general vertical direction (Fig. 29), 

 eventually thickened at its margin (Fig. 30) ■ In these sections its base 

 is indented by a small fissure, which in the last is prolonged as an axial 

 pale line rather more than through half the width of the anlage. 



12 millimeter embryo, No. 78 {Figs. 122-128).— This embryo is 

 hardly more advanced than that of 11. 5 millimeters. It is almost 

 perfectly oriented in the transverse plane, which renders unnecessary 

 the after all not very difficult task of allowing for obliquity in sections 

 where it is desired to distinguish between a keel and a flange. The 

 sections are 20 m in thickness ; alternate ones of the anlage of the right 

 side are given, together with one of the intermediate segment of the 

 sulcus, 100 fi prelingual in situation. In this section (Fig. 122) the 

 sulcus' is a slightly deepened angle, its epithelium very slightly thick- 

 ened. The Ungual sections show a flange or blind fold with a pale 

 a.xial streak, gradually increasing to a maximum (Figs. 123-125) and as 

 graduallv decreasing caudad (Figs. 126-128). The maximum is 

 attained' in the region of the submaxillary gangUon; the latter 

 from its situation and size is seemingly able to account, at least in part, 

 for the apposition of the walls of the fold. Craniad of the lingual 

 nerve the flange gives place to an angular sulcus with a keel attached. 

 The keel alone was present in the 11 millimeter embryo, and extended 

 over the whole of this region. It therefore forms the actual free 

 border of the flange, which has simply carried it ventrad as the folding 

 occurred. The keel here forms, also, the cranial continuation of the 

 fold, a transition occurring near the Ungual crossing. 



No stages occur in our series intermediate between the conditions 

 observed in the 11 millimeter embryo and those of the 11. 5 and 12 

 millimeter embrvos. In none of them does the lingual sulcus appear 

 as a deep open 'furrow, nor show a gradual reduction of its lumen 

 by approximation of its walls, such as occurs in the parotid. The 

 formation of this segment of the sulcus and its retluction to form the 

 submaxillary flange appear, therefore, to be coincident and to con- 

 stitute a single process. 



