DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 239 



Dorsal to the line of the buccal sulcus, three discontinuous furrows have 

 now appeared : the secondary buccal sulcus, in the postdental segment 

 of the marginal cavity ; the superior alveobuccal, in the region of the par- 

 otid; and the superior alveolabial, which is preangular in position, and 

 corresponds to the anlages of the canine and incisor teeth. Ventrad in 

 addition to the inferior alveobuccal sulcus, the inferior alveolabial is now 

 present. This, like its fellow of the upper jaw, is situated far craniad. 

 It is a shallow furrow closely associated with the inferior dental anlage, 

 and has attached to its fundus a keel of epithehum which projects 

 into the adjacent mesenchyme. 



In subsequent stages the superior alveolabial, alveobuccal, and 

 secondary buccal sulci become confluent (Figs. 164, 165), mainly 

 by the extension of the intermediate element in both directions. In 

 the embryo of 25 millimeters the superior alveobuccal sulcus has 

 extended caudad into continuity with the secondary buccal sulcus ; 

 craniad as the angulus oris is approached it loses its angularity and 

 becomes a rounded curve where the horizontal epithehum of the roof 

 passes into the nearly vertical layer of the lateral wall. In the plane 

 of the anguh oris and craniad it again becomes well defined. Here 

 the roof makes a rectangular junction with the vertical lateral wall 

 which descends to the buccal sulcus. Still farther craniad a distinct 

 furrow appears, the superior alveolabial sulcus, which rapidly deepens 

 into a cleft opposite the canine tooth and again abruptly diminishes 

 opposite the incisors. The fundus of the sulcus is prolonged into the 

 mesenchyme by an epithelial crest, which, splitting, serves to deepen 

 the cleft and to assist in freeing the lip. In the presence of tliis keel 

 the alveolabial sulci differ from the alveobuccal, which are formed by 

 simple bending in the oral epithehum, and subsequently deepen as 

 the alveolar processes enlarge and the cheeks become vertical. Simi- 

 lar conditions obtain in the region of the lower jaw and ventral hmit of 

 the vestibule, with the difference that the inferior alveolabial and 

 alveobuccal sulci never become confluent, but are permanently sepa- 

 rated by a diastemal fold which extends transversely from the margin 

 of the hp to the socket of the canine tooth (Figs. 109, 114). Caudad 

 the inferior alveobuccal sulcus approaches the buccal sulcus, but 

 becomes shallow and disappears near the border of the masseter, 

 not improbably in consequence of the presence of the muscle. 



