28o DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



diminishes caudad, so that in a few sections both flange and sulcus 

 have disappeared (Fig. 138). 



The sprout has lengthened and is directed ventrad, caudad, and lat- 

 erad, toward the mesenchymal thickening (j2) which it has now reached 

 (Fig. 138). In this course it passes caudad of the Ungual nerve and 

 its gangUon, which accompanies it with a sheathhke extension (Fig. 

 137, 40). The extremity of the sprout is enlarged, retort shaped, and 

 lies at about the level of the caudal border of the mylohyoid. 



The model of a submaxillary corresponding in general to this, but 

 with a less degree of cranial extension of its duct — a process variable 

 in its rate — is shown in Fig. 139 from an embryo of 15 millimeters. 

 The anlage has lost the wavelike form of its earher stage, and is now a 

 somewhat triangular object with a concave caudal border. The sprout 

 is attached to the region of greatest width of the flange, and thus is 

 seen to correspond to the early thickening of the margin which appears 

 at a similar point. Craniad the ventral border ascends rapidly to the 

 lingual sulcus, where it extends but little beyond the lingual crossing. 

 The portion of the fl:inge caudal to the attachment of the sprout pre- 

 sents two shght constrictions, which partially divide it into an element 

 attached to the lingual sulcus, the postglandular flange, and a portion 

 intermediate between that and the sprout. The greater subhngual 

 anlage is also present to the lateral side of, and separate from, the sub- 

 maxillary, immediately dorsal to the lingual nerve (jj). 



We may now, on the basis of these findings, attempt an interpretation 

 of the processes at work in the formation of the submaxillary anlage. 

 The order of events is : first, the separation from the general placode- 

 like thickening of the oral epithelium of a keel extending along the 

 caudal and the greater part of the intermediate segments of the lingual 

 sulcus; second, the formation in the region of the submaxillary gang- 

 hon of a flange; third, its extension craniad, diminisliing the while, 

 until in the intermediate segment of the sulcus it finally ceases to be 

 formed and only the keel persists; fourth, the displacement of the 

 keel to a lateral parietal position. 



The early solution of continuity in the epithelial thickening of the 

 floor of the mouth is associated with the rapid expansion of the area. 

 A gap between the alveolingual thickening and the inferior dental 

 anlage is estabhshed in the period of 9.5 to 10 nrilfimeters. In embryos 



