284 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



and increasingly so craniad. Here we are dealing with a process al- 

 ready observed in the case of the parotid and of the orbital inclusion, 

 wliich was there attributed to unequal growth in the walls of the sulcus 

 and consequent shifting at its fundus. In the case of the Ungual sul- 

 cus there appears to be a further element in the nature of inrolling. 

 We have now reached a point where this is unequal as regards the 

 mesal and lateral walls of the sulcus, the contribution from the tongue 

 exceeding that from the alveolingual region, either absolutely or in 

 capacity for growth. The alveoUngual region broadens slightly, 

 wliich fa\-ors the ^'iew of a lessened inrolling. In any event the keel 

 has now become parietal. It does not extend now as a recognizable 

 element along the cranial segment of the sulcus, but gradually is 

 formed in a caudocranial direction, advancing by slow and unequal 

 increments from stage to stage. 



This advance by a keel, which is not fundal, but lateral parietal in 

 position, is characteristic of all the later stages of the anlage. As 

 the sections are followed craniad the flange diminishes gradually. 

 From the first the anlage has been a keel of tliickened epithelium to 

 which a flange has been added. The keel forms the free border of the 

 compound structure, and proliferating occasions the enlargement of 

 the border of the flange and gives rise to the free-growing sprout. 

 The proliferation extends craniad, using the flange as a guide or scaf- 

 fold. But the lingual and prelingual segments of the sulcus have 

 begun to deepen, tending to drive the fundus deeper, or rather to form 

 a new fundus mesad of the keel, which, therefore, assumes a parietal 

 position in the lateral wall. The lateral bend of the anlage (Fig. 137), 

 with its consequent displacement of the free border, also favors the 

 change by altering the direction of the line by which the proliferation 

 is advancing, and causing it to impinge upon the lateral wafl of the 

 sulcus. The direction of this line is craniad and slightly dorsad; that 

 of the fundus almost horizontal. The keel of proliferation continuing, 

 this hne becomes more and more dorsally placed in the lateral wall 

 as the process advances craniad, and, until it comes to rest, is in each 

 successive stage carried farther from the fundus. This in late stages 

 causes it to open upon the summit of the plica sublingualis, the mesal 

 surface of which is the lateral wall of the lingual sulcus. 



In the 20 miUimeter embryo, No. 241, and in a few others of about 



