DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 285 



this period, a small keel is present attached to the lateral wall of the 

 lingual sulcus in its cranial segment, unconnected with the submaxil- 

 lary keel. In this embryo on the right side it extends from the fren- 

 ular section 40 n caudad. It is in line with the submaxillary keel, but 

 separated from it by a wide sagittal interval. The same formation 

 occurs in the human embryo both in the submaxillary and sublingual 

 lines. Here, then, we have the possibility given of the formation of 

 the duct by fusion of distinct elements. Yet this departure from the 

 norm cannot be considered of more than slight degree. In the ad- 

 vance of tliis duct, and of others, we are dealing with a process of pro- 

 liferation which advances craniad, not a bodily displacement of mate- 

 rial. As the duct advances the latent glandiferous functions of more 

 cranial segments of the oral epitheUum are successively aroused, and 

 the keel is formed by the acti\dty of the segments to wliich it is at- 

 tached. In these outlying keel formations we meet merely a distur- 

 bance of the time element ; epithelium destined to produce a keel prohf- 

 erates at an earher period than is usual. In this there is a strong 

 suggestion that the ducts are advancing along glandiferous lines, which 

 in some ancestral form yielded series of small glands, the crowded 

 anlages of which are now compounded and fused to form the duct. 

 An occasional recrudescence of their ancient independence finds ex- 

 pression in the accelerated appearance of a portion of the keel, as in 

 the case here considered, which is no more than a sUght disturbance 

 of the rhythm of the process, a deviation from the strict sequence of 

 events in time. 



That the proliferation process of the submaxillary is in reality inde- 

 pendent of the lingual sulcus, and that its duct is in no sense its sepa- 

 rated fundus, is shown clearly in a few embryos where the intermediate 

 segment of the sulcus fails to advance beyond a condition of sHght 

 angulation. In Fig. 150 the usual condition of the intermediate seg- 

 ment is shown in a 19 millimeter embryo. There is a deep lingual 

 sulcus directed ventromesad and the keel of the submaxillary is at- 

 tached to its lateral wall. In Fig. 147, also from a 19 millimeter em- 

 bryo, the same region is shown. The lingual sulcus is reduced to a 

 mere angle, lateral to which the submaxillary keel is attached to the 

 floor of the alveolingual region Here is clear evidence that the sulcus 

 as such does not supply the material for the advance of the duct. 



