44 THE DEVELOPMENT OF THE SALIVARY GLANDS IN MAN 



The orbitoparotid interval increases greatly in later stages. Meas- 

 uring in the 20 millimeter embryo 53-66.5 /it, it has attained a length of 

 300 /x in that of 22 millimeters and in Chievitz's embryo of 10 weeks. 

 That this is not due to reduction of the inclusion is seen by a compari- 

 son of its length in the 20 millimeter embryo and Cliievitz's of 10 

 weeks, 432/1 against 680 /t. The displacement appears, then, to be 

 due to growth of the interval itself. The inclusion, however, varies 

 within wide limits in these older embryos, from 249 fi in the 22 milli- 

 meters to I millimeter in that of Chievitz of 12 weeks. Its later 

 stages and ultimate fate have not as yet been investigated. 



The question of the origin of the parotid, whether by a simple sprout, 

 or by the formation of a fold with subsequent budding, must still await 

 a definitive solution as far as the human embryo is concerned. The 

 problem is one of considerable delicacy, being complicated by the site 

 of the anlage at the line of union of two sloping epithelial planes, the 

 roof and floor of the mouth and further, by the early appearance of the 

 periderm, the bulging nuclei and pale cell bodies of which disturb 

 the ental contour of the epithelium and in a fold obscure the line of 

 the obliterated lumen. Further, in gland sprouts we find the central 

 cells possessed of the staining properties of periderm, so that in a given 

 case it may well be impossible to decide, whether a paler a.xial line repre- 

 sents layers of periderm in contact, or the central cells of a solid sprout 

 undergoing an analogous cytomorphosis. Finally, active prolifera- 

 tion of cells along a linear area may produce a slight fissure-like inden- 

 tation of the ental surface of an epithehum in a region where no furrow 

 has pre\^ously been observed {e.g. the greater sublingual anlage of the 

 cat). The final settlement of these questions can only be expected 

 when a study of this anlage is undertaken on the basis of a complete 

 series of embryos at the requisite stages. But when the proof of the 

 inception of the parotid by a fold is finally brought, which on grounds 

 of analogy with conditions in the cat may be e.xpected, we shall again 

 be met with difficulties in assigning to the fold its quantitative value 

 as against the claims of the sprout, from which undoubtedly the whole 

 periphery of the gland and a part of the duct are derived, and this in 

 large measure because of the almost insuperable difficulty of distin- 

 guishing in a fundal anlage between a crestlike proliferation and a 

 blind fold. The point in this instance is really a minor one, for both 



