296 DEVELOPMENT OF SALFVARY GLANDS IN THE DOMESTIC CAT 



(Figs. 144, 145V On the left the lingual sulcus is absent except in its 

 cranial segment, which the anlage of the submaxillary has not yet 

 reached. On the right the intermediate portion is well developed, 

 3'et the two submaxillaries have reached corresponding points in their 

 advance, and distance the greater sublingual to the same degree. 



In the stages represented by the embryos between 20 and 51 milli- 

 ■ meters length the duct continues its advance by the same process, the 

 proliferation of a keel and its separation by constriction, and it con- 

 tinues to lag behind the submaxillary. The keel in these embryos is 

 usually indented by a slight fissure on its oral surface at least in some 

 of its sections. The degree varies from a slight concavity to a fissure 

 which in a very few cases causes the anlage to resemble a flange; a 

 good example of this maximum condition is shown in Figs. 148, 151. 

 Only rarely does the fissure extend through the whole length of the 

 flange and it is almost uniformly absent from the most cranial sections, 

 which thus continue to resemble the early condition of the anlage. 

 WTiile these fissures are at any stage inconsiderable in sagittal extent 

 as well as depth, and always confined to the keel, which is itself short, 

 yet in a composite of the whole period of advance of the greater sub- 

 lingual, they would serve to plot a Une extending from the middle of 

 the gutter at the lingual crossing to a cranial point nearer the mesal 

 than the lateral boundary of the region, corresponding in position and 

 direction to the intermediate sulcus of the human embryo. 



In the embryo of 51 miUimeters the keel has disappeared, and the 

 lumen of the duct can be followed to the oral epithelium. Being 

 lateral in situation, it reaches the convexity of the plica sublingualis 

 earlier than the submaxillary, and in the 70 millimeter embryo is 

 attached to its lateral aspect. 



The advance of the greater subhngual in the period between 25 

 and 51 miUimeters is shown by the table on follo\ving page, the same 

 points of measurement having been used as in the preceding one. 



The distal growth of the greater sublingual is sluggish for a long 

 period. In embryos of 1 7 millimeters the caudal extremity of the keel 

 is enlarged and spherical. In those of 18 millimeters it forms a short, 

 horizontally directed sprout, which grows distad below the alveolin- 

 gual gutter to the mesal side of the lingual gangUon, which is grooved 

 to receive it, and against which its fundus rests. In the embryos of 



