DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 24 1 



standpoint the border of the masseter appears as a disturbing factor in 

 the development of the maxillomandibular plane. The same changes 

 occur in the oral epithelium cranial and caudal to it, and at a later 

 period, regularly as regards the sulcus, rarely as regards the fold, 

 involve the segment opposite the muscle, and become continuous. It 

 is ditBcult to escape the impression that a separation in primitively 

 continuous structures has here been occasioned by developmental 

 exigencies, which nevertheless the momentum of heredity from re- 

 mote non-mammalian ancestors is sufficient to overcome, at a later 

 period in the case of the sulcus, as a rare variant in that of the 

 flange. If this be the explanation of the temporary disjoining of the 

 superior alveobuccal and secondary buccal sulci, it follows that united 

 they constitute a vaUd morphologic line and that the derivatives of 

 its respective segments form a single series ; the superior alveobuccal 

 and the orbital glands are, therefore, homodynamous. 



Once estabhshed the alveobuccal sulci form the dorsal and ventral 

 limits of the vestibule. Between them as they deepen the wall of the 

 cavity gradually becomes vertical by the opening out of the lateral 

 portion of the maxillomandibular plane and the obhteration of its 

 lateral border, the buccal sulcus. This becomes broad and rounded 

 and in the 51 millimeter embryo (Fig. no) is represented only by a 

 moderate convexity of the lateral wall, while in the 70 miUimeter 

 embryo it has disappeared in the orbitoparotid interval (Fig. 115), 

 though persisting near the angulus (Fig. 114). The process is illus- 

 trated in Figs. 157-160 from embryos of 12 miUimeters to 70 milli- 

 meters in length. These sections are preparotid in position and show, 

 accordingly, a region of the vestibule where the dorsal component 

 of the cheek tends to equal or exceed that derived from the floor. 

 It is evident that the lateral wall of the vestibule is formed by the 

 elevation to a vertical position of the regions lying between the alveo- 

 buccal and the buccal sulci, and that in consequence of the unequal 

 extent of these regions in the roof and floor of the mouth, their con- 

 tributions to the cheek must be unequal. In fact, the greater part of 

 the latter is formed at the expense of the floor, as Chievitz was the 

 first to demonstrate. This is true, however, of the caudal portion of 

 the vestibule only. Craniad, in consequence of the ventral inclination 

 of the buccal sulcus, the roof forms an increasing proportion of the 



