2 20 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



of the type of embryo 216 (Fig. 45) are relatively blunt and separate 

 early. 



The time of separation of the caudal extremity of the inclusion varies 

 within wider limits. The earliest separation observed was in an 

 embryo of 18.5 miUimeters; the latest retention of the caudal attach- 

 ment in one of 35 millimeters, on one side only. In the embryos of 

 19-21 miUimeters it is free rather oftener than not. In those of this 

 period in which the attachment persists, it is situated considerably 

 ventrad of the secondary buccal sulcus on the ventrolateral wall of 

 the palatomandibular plane. Here the oral epithelium bulges in a 

 small conical process to meet the tip of the inclusion. A thick 

 stratum corneum i^ present, the ental contour of which is a httle 

 concave opposite the attachment of the inclusion. There is a 

 well-marked constriction at the junction of the inclusion and the 

 oral epithelium. The appearances are suggestive of traction on the 

 oral epithehum, resulting from the displacement laterad of the inclu- 

 sion, as mesenchyme accumulates between it and the oral epithe- 

 lium. In a few cases the caudal attachment persists to a late period. 

 It is present in the 25 millimeter and the 35 millimeter embryos, in 

 each on one side. In the 51 millimeter embryo on the left side the 

 constriction is complete, but contact is still retained. In all these cases 

 the extent of the attachment is minimal, rarely of greater length than 

 one section. The possibility of extension caudad by proliferation has 

 already been alluded to. If it occurs to a degree adequate to explain 

 the differences in the time of separation, it must be correlated in rate 

 to the process of separation with great nicety, for the length of the 

 attachment is remarkably constant in the embryos ^studied. Of the 

 free growth of a caudal process, the only evidence is the occasional 

 finding of a free ultimate section or two of the inclusion, while the 

 penultimate portion is still attached. 



The orbital inclusion, as soon as separation is completed in any 

 segment, begins to be displaced laterad towards the internal pterygoid 

 muscle, with the ental surface of which it comes ultimately into juxta- 

 position. Its topography at 18.5 milhmeters, the earliest example 

 of its complete separation, is shown in Fig. 103. The pars lata (7) Ues 

 farthest laterad, resting in a small concavity of the surface of the ptery- 

 goid (74) vertically above the mandible (5^). From this point the 



