346 MAMMALIAN ALVEOLINGUAL SALWARY AE.EA 



tion is at all marked. The alveolar sulcus is a shallow conca\'ity, lined 

 with thickened epithelium. It has a general sagittal course, but ap- 

 proaches the Ungual sulcus caudad, where the latter becomes deep. 



In a second embryo of 15 milhmeters (Princeton Collection, No. 210) 

 the subma.xillary is slightly more advanced in development, and the 

 anlage of the sublingualis major has appeared. The beginning forma- 

 tion of a flange by the apposition of the walls of the lingual sulcus is 

 indicated ; the sulcus is somewhat less deep and its fundus has more 

 the character of a fissure ; the solid epithehum of the submaxillary 

 anlage is increased in height (Fig. s,y). In profile the anlage is wave- 

 Hke ; it is postUngual in situation ; lateral to it is the bulky submaxil- 

 lary ganghon. The lateral Up of the Ungual sulcus has the same con- 

 tour as in the preceding embryo. Here the anlage of the subUnguaUs 

 major appears as a soUd ridge subhemispherical in section (Fig. 3, //). 

 It has a length of 75 /x. The cranial extremity is 105 m behind the 

 Ungual nerve, the caudal is opposite the deepest portion of the sub- 

 maxillary. The anlage diminishes craniad, where it is attached about 

 midway between the lingual and alveolar sulci, to the convex floor of 

 the alveoUngual region. It is thus absolutely independent of the sub- 

 maxillary, which it only approaches caudad in the region where the 

 flange has begun to be formed. The alveolar sulcus resembles that 

 of the preceding embryo. Meckel's cartilage is now better defined 

 craniad, and the termination of the sulcus is directly dorsal to it. 



In an embryo of 16 milhmeters (Princeton Collection, No. 217) 

 there are important changes. The anlage of the submaxiUary has 

 increased in size and now has a triangular profile, its caudal border 

 being nearly vertical, a conformation which recalls Hammar's descrip- 

 tion of its early condition in man. In section (Fig. 4) the Ungual sul- 

 cus is seen to be still deep, its fundus fissure-Uke. The epitheUum of 

 the submaxillary (7) has increased in size, is retort shaped, and is 

 sUghtly constricted as it joins the sulcus. A periderm Une in its axis 

 can hardly be distinguished. The anlage of the sublingualis major has 

 a length of 105 /x; its cranial extremity extends to within 40 fj- of the 

 lingual nerve. Its caudal extremity retains its position in the lateral 

 lip of the Ungual sulcus, while craniad and in the greater part of its course 

 it is attached to the lateral wall of the sulcus near its fundus (Fig. 

 4, //). It is evident, therefore, that incident to the formation of the 



