196 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



to the buccal sulci. The midline is marked by the depression between 

 the mandibular processes at their cranial extremity. At the plane of 

 the anguli oris the tuberculum impar appears in this depressed area 

 (Fig. 5). and farther caudad forms a prominent triangular elevation, 

 separated from the maxillary processes by well-marked concavities 

 (Figs. 6, 7, 8, 41). Caudad it is continuous with the radix lingua^ with- 

 out demarcation, the foramen ccecum and thyreoglossal duct having 

 completely disappeared. The mandibular processes form prominent 

 convexities in the oral cavity by their mesal borders, diverging and 

 diminishing in prominence from the s>Tnphysis towards the hrst 

 entodermal pouch. Their oral surface in its more lateral portion is 

 nearly horizontal at the angulus oris (Figs. 5-8. 40),. Caudad it 

 presents a slight concavity. 



As a whole the mouth narrows from the anguh oris to the first en- 

 todermal pouch. Its lateral limits, the buccal sulci, are of especial 

 importance in the study of the salivary glands. At this stage they 

 are short, extending from the angulus oris to the origin of the first 

 pouch. In the greater part of their extent they are deep and well 

 defined ; caudad they become broad and shallow and are lost as the 

 pouch begins to define itself. The buccal sulci acquire during develop- • 

 ment a rather complex system of curves. At this period they ascend 

 slightly as they are followed caudad. In the horizontal plane they 

 converge throughout their whole extent but most rapidly in the cranial 

 third of their course, describing a gentle curve with the concavity 

 turned laterad and caudad. At the anguli oris (Fig. 5, 2) they pass 

 transversely laterad into continuity with faint surface furrows which 

 run but a short distance caudad. These furrows afford the only 

 boundary between the ma.xillary and mandibular processes caudad of 

 the angulus oris. 



Along the buccal sulcus the epithehum is thickened, the cells are 

 higher, and two or three irregular rows of nuclei are present. The 

 thickening diminishes very gradually mesad, extending along the floor 

 of the mouth to the summit of the maxillary convexity, and on the 

 roof a somewhat shorter distance, not quite to the nasal and tubo- 

 tympanic sulci (Figs. 5 and 6). The portion of the oral cavity lined by 

 this thickened epithelium presents, as the pharynx is approached, a 

 degree of conformity of its roof and floor (Fig. 6). At the angulus 



