344 



M.«MMAL1AN ALVEOLINGUAL SALIVARY AREA 



always be absolute, that not all of the material of the mesal portions 

 of the field would in all cases be incorporated into the lines of the sub- 

 maxillary and subungualis major, but that in some embryos rudiments 

 of glands might appear between the duct lines and the diffuse field of 

 lesser sublinguals. .In the 20 millimeter embryo such were present 

 along the intermediate sulcus and also between it and the Ungual fur- 

 row in the form of small epitheUal thickenings, Uke short ridges, but 

 not enlarged at their distal (aboral) extremity, as is the case in active 

 sprouts. 



It remains to consider the process by which these several elements 

 become oriented in the dorsoventral plane, so that the primitively 

 mesal submaxillary becomes ventral, the lesser subUnguals dorsal, 

 while the Bartholinian element retains its intermediate position. This 

 is accomplished by the concomitant displacement ventrad of the sub- 

 maxiUary duct after its separation from the oral epitheUum, and the 

 mesal shift of the BarthoUnian duct, while the elevation of the lateral 

 portion of the alveolingual region, attending the enlargement of the 

 alveolar process and the appearance of the arcus palatinus, accounts 

 for the dorsal position of the orifices of the Rivinian glands. This 

 rearrangement of the several elements affords a clue to the apparent 

 discrepancies in the history of the BarthoUnian element in its relation 

 to the submaxillary gland, its attachment to which, in such forms as 

 man and the pig, being conceivably no more than the result of a mesal 

 displacement of such an independent anlage as occurs in the cat, 

 accomplished secondarily by a movement in toto of the epitheUum of 

 the alveolingual region. This supposition is further supported by the 

 formation of a blind fold or flange along the Ungual sulcus, incident 

 to the appearance of the submaxillary anlage; the material for this 

 must evidently be derived, so far as its lateral lamina is concerned, 

 from the surface epithelium of the alveolingual gutter. Could a form 

 be found in which the BarthoUnian proliferation was established prior 

 to the formation of the submaxiUary flange, actual proof of the shift 

 might be forthcoming. In view of the fact that in the earliest of 

 the pig embryos described by Chie\'itz (22 milUmeters) the anlages of 

 both glands had attained a considerable size, and, further, that the 

 flange or crest of the submaxillary was of great depth, it -seemed 

 desirable to examine younger embryos, with a view of ascertaining 



