DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 1 97 



each has an independent relief, the roof sloping to the buccal sulcus, 

 the floor approaching it horizontally (Fig. 5). 



The mandibular nerve descends laterad to the sulcus near its caudal 

 end, a small quantity of mesenchyme intervening (Fig. 6, 6^). Here 

 the buccal sulcus and adjoining portions of the oral cavity are tilted 

 dorsad, as though the presence of the nerve were felt through the in- 

 tervening mesenchyme as an obstacle to further lateral extension. 

 Further effects that may be attributed to such resistance are the in- 

 creasing conformity between the floor and roof, and a beginning ap- 

 position of the walls of the buccal sulcus, with concomitant reduction 

 of its lumen to a minute fissure. In this embryo the process has 

 barely been initiated and is expressed only by an increased acuteness 

 of the angle formed on the ental surface of the epitheHum. 



These effects become more pronounced in older embryos. Unfor- 

 tunately, owing to the spiral twist which is marked at this stage, the 

 sections through the head are usually oblique, and that to a varying 

 degree, which renders a direct comparison of dimensions as a rule im- 

 practicable. An embryo of 10 millimeters, No. 237 ofour series, is oriented 

 almost perfectly in the transverse plane, and though the sections are 

 considerably inclined dorsoventrally, permits a comparison of its 

 transverse dimensions with those of the 8.5 millimeter embryo. The 

 camera lucida outlines of Figs. 9 and 10 are reproduced upon the same 

 scale as Figs. 1-8. It will be seen that at the angulus oris the diameter 

 has increased about one-fifth, while it has remained stationary between 

 the mandibular nerves. The interval between the nerves has not 

 increased, although the head as a whole is broader. The oral cavity 

 adapts itself to the space thus determined for it by a dorsal tilting of 

 its lateral portion. As a result the buccal sulci become arched, as- 

 cending slowly from the anguli oris to their crowns opposite the 

 mandibular nerves, and thence making an abrupt descent to their ter- 

 minations caudal to the nerves. Their horizontal curvature is also 

 increased, the caudolateral concavity more pronounced. Meanwhile 

 the fold along the buccal sulcus in the vicinity of the mandibular nerve 

 has increased in degree and extent (Fig. 10, 6). It surmounts the 

 buccal sulcus as a solid flange, the base of which is indented by a small 

 fissure, the remnant of the lumen of the sulcus. Craniad the fissure 

 widens and all trace of the fold is quickly lost. In this fold we meet 



