DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 1 95 



glands. The development of the oral cavity is here followed, as a 

 whole, to the stage of 13.5 millimeters. From that period the individual 

 glands are discussed separately, first those of the vestibule, then those 

 of the cavum oris proprius. 



THE ORAL CAVITY IN EMBRYOS OF 8.5 MILLIMETERS TO 13.5 MILLIMETERS 



In the embryo of 8.5 millimeters the oral cavity forms a wide, shallow, 

 dorsoventrally flattened vestibule to the pharynx. Craniad its roof 

 passes by a gradual curve into the surface of the head. The widely open 

 diverticulum of the hypophysis extends from a point slightly craniad 

 of the mandibular symphysis to end just caudad of the plane of the 

 anguli oris. From this it appears that we are deahng with a stage 

 where as yet the nasal fossae and the material for the formation of the 

 palate lie beyond the arch of the mandibles, which in this cavity corre- 

 spond to the hypophysial and methypophysial segments of the roof, 

 i.e. in general to the nasopharynx. The general features of the region 

 are shown in camera lucida outlines in Figs. 1-8. 



The mouth in section has the shape of an elongated lozenge laid on 

 ■ its side ; both roof and floor show a shght but independent modeUng. 

 The roof in the middle presents a deep V-shaped gutter continued from 

 the hypophysis into the pharynx, where it attains a ma.ximum in the 

 plane of the first entodermal pouch, and thence diminishing is lost be- 

 tween the pouches of the fourth pair. From this gutter the roof slopes 

 almost uniformly to its union with the floor at the buccal sulcus (Figs. 

 5 and 6). Two pairs of sulci diverging from the hypophysial region, 

 craniad and caudad respectively, interrupt this descent. The cranial 

 pair, the nasal sulci, are continued into the nasal pits, intervening be- 

 tween the frontal process mesad and the ma.xillary and faintly in- 

 dicated outer nasal process laterad (Figs. 1-5, 82). The caudal pair 

 of furrows are the tubotympanic sulci of Moldenhauer. They begin 

 caudad to the hypophysis and are continued into the dorsal borders 

 of the first pouches (Figs. 6, 7, S6). The nasal and tubotympanic 

 sulci are not at this period continuous. 



The floor of the oral cavity is formed by the mandibular processes 

 and the tuberculum impar. The mesal region is depressed relative to 

 the lateral portions, which extend in a generally horizontal direction 



