32 THE DEVELOPMENT OF THE SALR'ARY GLANDS IN MAN 



middle of which a line of less deeply staining periderm cells extends 

 between the lumen of the mass and the oral cavity. The whole 

 formation extends about 146 m from the angulus oris, though owing 

 to the obliquity of the sections and the curve of the sulcus the measure- 

 ment cannot be considered exact. In the sections immediately cranial 

 to those showing the closed fold, an indefinite mass of cells situated 

 in the mesenchyme lateral to the sulcus is thought to be the man- 

 dibular nerve. The nerve tissue throughout is in very bad condition, 

 but this object resembles areas elsewhere that from their situation can 

 be recognized as parts of peripheral nerves. 



3. Hammar. Embryo of 11. 7 millimeters, N.L. The middle third 

 of the sulcus buccalis presents a small shallow furrow, the "sulcus 

 parotideus." 



These three embryos present successive stages of the transformation 

 of a fold into a cylinder of cells by a process of constriction reducing 

 the lumen to a fissure or line at the point of constriction. Hammar 

 does not state explicitly that his anlage contains a lumen, but that 

 it does so may be inferred from his note upon his next older embryo. 

 The situation of the fold with reference to the angulus oris requires a 

 word of explanation. It occupies at the outset a small bit of the 

 cranial end of the sulcus ; it then involves the whole of its cranial 

 segment ; in the third embryo, only its middle third. Two explana- 

 tions offer : the fold at its cranial extremity may have opened again 

 into continuity with the. oral cavity; or, on the other hand, the 

 sulcus buccaUs may have lengthened by increment from in front. In 

 no case unfortunately has the relation of the fold to the mandibular 

 nerve been clearly established. Hammar interprets the fold as the 

 anlage of the parotid. He has not proved this to be the case, as his 

 next embryo is of 17 millimeters length and presents an advanced 

 stage of the parotid, too wide a gap in the series safely to be spanned 

 by an inference. It is by no means clear that the fold and sulcus 

 parotideus of Hammar are not incident to the formation of the orbital 

 inclusion in whole or in part. The general mode of formation of the 

 anlages of the salivary glands in the forms as yet studied corresponds 

 so closely, that conditions known in one species should not be without 

 weight in the interpretation of a fragmentary series of another. In 

 the cat the orbital inclusion is formed in a manner so similar, and 



