46 THE DEVELOPMENT OF THE . SALIVARY GLAXDS IN MAN 



all trace has disappeared in the 22 millimeter, where the attachment 

 is already parietal. In older embryos the distance between the 

 parotid and angulus oris again increases, and in Chievitz's 12 weeks 

 embryo is 1.26 millimeters. This second displacement appears due 

 to growth in the proparotid segment of the cheek, and is associated 

 with obliteration of a portion of the buccal sulcus, and extensive 

 changes in topography. 



Further evidence of the addition to the parotid of a pro.ximal seg- 

 ment is afforded by the site of its junction with the orbital inclusion in 

 Chie\dtz"s embryo of 12 weeks. Here the two elements are joined at 

 the cranial border of the masseter. Their continuity must ha\-e been 

 achieved before separation from the oral epithelium, by extension of the 

 constriction of the orbital inclusion over the whole orbitoparotid in- 

 terval, into continuity with the usually distinct process which frees 

 the parotid. The parotid duct of this embryo distal of the union with 

 the inclusion would then be referable to the sprout. The segment 

 intervening between the jimction with the inclusion and the oral epi- 

 thelium, that is, the whole promasseteric segment of the duet, is of 

 secondary formation. More information is desirable as to the mode 

 of this process, and especially as to whether it may continue after the 

 parotid has lost its sulcal position. The e\-idence obtainable from the 

 20 millimeter embryo has been stated, and seems to give preference 

 to the proUferation of a crest, rather than to the formation of a blind fold 

 as the source of this material. The primitive position of the parotid 

 duct is submasseteric in man as in other mammals (Chievitz), a posi- 

 tion which is retained in ungulates. Subsequently it attains a horizon- 

 tal higher position, by a dorsal displacement over the surface of the 

 masseter and a straightening of its cur\'e. 



THE .A.LVEOLINGTJ.A.L region; its sulci AND THEIR DERR'ATR'ES 



In human embryos from about 15 to 22 millimeters in length, the 

 alveohngual region (Fig. i , 20) is a broad gutter into which projects the 

 palate process {25). Here the epithelium forms a fold, as it passes 

 from the tongue laterad to a prominent convexity, produced by an 

 accumulation of mesenchyme between Meckel's cartilage and the 

 floor of the mouth. This convexitv is Umited laterad bv a shallow 



