THE DEVELOPMENT OF THE SALIVARY GLANDS IN MAN 43 



later stages, and the failure to find it in earlier ones, appears due to the 

 fact that with the extension of the parotid eaudad along the surface 

 of the masseter, the two structures come into the same sections, one 

 ectad and one entad of the muscle. In younger embryos when the 

 parotid has not begun its caudal growth, but projects ventrolaterad 

 from the buccal sulcus, it disappears from the sections in the orbito- 

 parotid interval, before the anterior extremity of the inclusion is 

 reached. An observer intent upon the parotid would have no occasion 

 to follow his sections farther than that anlage extended, and unless he 

 did so woidd not come upon the inclusion. The possibihty of confus- 

 ing the two derivatives of the buccal sulcus is easily accounted for, 

 if only one was sought and the whole length of the sulcus was not 

 examined. Finally, Hammar's description of the anlage in his 17 

 millimeter embryo as a slender duct cannot be made to harmonize 

 with conditions in the 20 millimeter embryo of the Columbia Collection, 

 where a soHd retort-shaped mass is present with no free duct, but with 

 signs of beginning separation at the caudal margin of its attachment. 

 The order of events is then, first, the estabhshment of a sprout, and 

 second, the formation of a proximal portion of the duct by con- 

 striction. 



The orbital inclusion once separated from the oral epithelium is 

 gradually displaced laterad, until it comes to lie close to the muscles of 

 mastication. Its caudal extremity, sUghtly enlarged, rests against 

 the internal pterygoid. Its cranial extremity, which also tends to be 

 enlarged, may run out into a tapering process (Bujard) or may even 

 be continuous with the parotid duct (Cloievitz). The simplest explana- 

 tion of these variants is to suppose the fold of origin to extend farther 

 craniad, encroaching upon the orbitoparotid interval, wliich in Chie- 

 vitz's case has evidently given rise to an orbitoparotid bridge, which, 

 separated in its entirety, connects the parotid with the orbital inclu- 

 sion. On this supposition it is possible that Hammar's embryo of 

 II. 7 millimeters actually presents this continuity, though more in- 

 formation upon this stage and those but httle older is greatly to be 

 desired. A hke connection has as yet been found only in three em- 

 bryos of the pig (Weishaupt 2, Columbia Collection i) and one of a 

 chevrotain. The cat, however, presents many variations in the length 

 of the interval and extension craniad of the orbital inclusion. 



