DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 225 



No. 100. It has a slightly greater sagittal length, extending from the 

 postangular bend somewhat nearer to the orbital fold. The mesen- 

 chyme condensation terminates ventrad of the pars lata of the orbital 

 inclusion. 



In embryo No. 78 a definite flange is formed. It has a sagittal 

 length of 100 A^ in the sections, increasing in width to its middle and 

 thence as gradually diminishing. At its maximum the lumen is oblit- 

 erated from the buccal sulcus to the small furrow before mentioned; 

 a pale line of interlocking periderm cells replaces the fissure. In the 

 other sections the flange extends a less distance mesad, where its base 

 is more or less indented by the remnant of the fissure. The flange as 

 a whole is concave ventrad, the concavity being occupied by the 

 mesenchyme condensation. Dorsad its convexity is evenly continuous 

 with that of the ectal surface of the roof of the mouth. In recon- 

 struction the parotid anlage forms a semicircular projection beyond 

 the general line of the buccal sulcus, which wliile in part the result of 

 compression, may also depend, even at its inception, upon an in- 

 creased rate of proUferation in the walls of the sulcus, the effects of 

 which soon become evident in the increased width of the flange. The 

 fold is reduced to a flange by an elevation of the floor meeting the roof 

 and obhterating its lumen from the buccal sulcus mesad. The order 

 of events is, first, a thickening of the mesenchyme and a displacement 

 of some of the nuclei of the epithehum, and second, the gradual eleva- 

 tion of the floor of the mouth. The mesenchyme thickening would 

 appear to be the active agent in the process. 



Between the parotid flange and the orbital inclusion the sulcus 

 recovers its lumen, but retains the primitive tliickening of the 

 epithelium. The condensation in the mesenchyme persists, but the 

 little furrow in the epithelium along its mesal border becomes 

 indistinguishable in the caudal sections of the flange. In this 

 embryo a definite, though short, segment (60 m) of unfolded sulcus in- 

 tervenes between the parotid and the cranial process of the orbital 

 inclusion, which we may term the orbitoparotid interval. It is, there- 

 fore, evident that two distinct folds are formed in the course of the 

 buccal sulcus, the orbital advancing craniad from the caudal segment, 

 and the parotid appearing at the postangular bend. In the thickened 

 epithelium connecting them and in the mesenchyme condensation we 



