THE DEVELOPMENT OF THE SALIVARY GLANDS IN MAN 45 



must here be due to proliferation of the oral epithelium, the question 

 being, whether we are to conceive this as chiefly localized in the roof 

 and floor of the oral cavity, or at the fundus of the buccal sulcus. In 

 the former case the simple proliferation of cells would enlarge the 

 buccal cavity transversely and displace its border, the buccal sulcus, 

 laterad in the direction of the resultant of the planes of growth. But 

 the advancing edge is subjected to the pressure of the enlarging maxil- 

 lary and mandibular processes, which tend to compress the advancing 

 angle, reducing its lumen to a fissure and finally obhterating it. The 

 soUd flange so formed would undergo displacement downward, were the 

 rate of growth in the maxillary process greater than in the mandibular 

 process. That this is indeed the case craniad seems indicated by 

 the overhanging of the maxillary process, and by the ectal position of 

 the superior dental ridge in reference to the inferior. But when the 

 parotid has assumed a retort shape, as in His's embryo Zw., the 

 role of the simple fold is at an end or at least comphcated by the ac- 

 celeration of cell proliferation at its free edge, as instanced by its 

 increased thickness laterad, so that the anlage can no longer be con- 

 ceived simply as a blind fold. The appearance leads us to attribute the 

 further development of the anlage to the free growth of the bud. In 

 the 20 milhmeter embryo the bud has already a pale center which is 

 not continuous with the periderm of the mouth, and therefore appears 

 to have developed in situ, as in the sprouts of the submaxillary in tliis 

 embryo. 



The formation of a pro.ximal portion of the parotid duct craniad of 

 the sprout is another and a later question. That the attachment is 

 for a time carried forward towards the angulus oris can be determined 

 by measurements. In the 20 millimeter embryo the anguloparotid 

 interval is 425.6 /^ ; in that of 22 milhmeters the distance has been 

 reduced to 240 /u.. The sagittal length of the attachment in the former 

 case is 53-66.5 /i, in the latter 60 fi. The absolute diminution of the 

 anguloparotid interval can only be accounted for by an absolute 

 addition to the duct craniad of the sprout. As is shown by the meas- 

 urements of the attachment, this formation must be accompanied by 

 a freeing of the new-formed element from the oral epithelium in a 

 caudocranial direction. This is accomplished by a process of con- 

 striction wliich is initiated in the 20 millimeter embryo and of which 



