240 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



The canine teeth thus serve to define in the adult the boundary 

 between two segments of the lip, the development of which differs. 

 Caudal of the canine, the space between the lips and jaw represents an 

 extension of the vestibule, with which it agrees wholly in mode of 

 formation, and into which during development its caudal portions are 

 progressively absorbed as long as the angulus oris continues to advance. 

 The fundus of the clefts are the alveobuccal sulci, both of wliich are 

 continued into the vestibule. The alveolabial sulci, the development 

 of which is associated with the presence of epithelial keels, are confined 

 to the region of the incisor and canine teeth. In the cat the superior 

 sulcus becomes confluent with the alveobuccal by the suppression of 

 the upper diastemal fold, which, however, is present in other mammals, 

 as, for example, the Suidae and some marsupials and edentates. 

 One of the latter, Tamandua bi\'ittata, affords an interesting confir- 

 mation of the view just stated of the alveobuccal sulci, that they repre- 

 sent a region of the mouth which is potentially vestibule. In this 

 form the angulus oris is placed far craniad, the vestibule greatly 

 lengthened, and the gape of the mouth correspondingly reduced. Both 

 upper and lower diastemal folds are well developed and attached to 

 the margin of the ma.xillaries caudal to the small canine teeth. Their 

 lateral extremities are attached to the angulus oris. Thus the whole of 

 the alveobuccal sulci are here included in the vestibule, and the angu- 

 lus has realized to the full its possibilities of cranial advance. 



The superior alveobuccal and the secondary buccal sulci agree in 

 being formed dorsal to the buccal sulcus after its fundus has been 

 obhterated to form a flange, in the case of the former the parotid, of 

 the latter the orbital inclusion. They appear, therefore, to define 

 equivalent areas of the maxillomanchbular plane, of which a portion 

 is sacrificed during development to the space requirements of the 

 muscles of mastication, \'iz. the orbital inclusion, the orbitoparotid 

 bridge, and the parotid flange. As in the flanges, so in the sulci, there 

 is a discontinuity in the process, which is incident at two points in the 

 course of the buccal sulcus, caudad in the region of the mandibular 

 nerve and its musculature, and craniad of the point at which the border 

 of the masseter intersects the line of the sulcus. Secondarily, the new 

 sulci become confluent and the dorsal limit of the vestibule is estab- 

 Kshed. The flanges as a rule fail to become continuous. From tliis 



