DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 21 7 



sulcus in its whole length ; the extremities are fundal in position, the 

 intermediate portion parietal. 



The 13 millimeter embryo (Fig. 31) is scarcely advanced beyond 

 these conditions, as far as the orbital inclusion is concerned. The 

 dorsal separating sulcus is well defined ; craniad it broadens and turns 

 laterad, towards but not reaching the buccal sulcus, defining the pars 

 lata and the as yet insignificant cranial process. Mesal to the separat- 

 ing sulcus the oral epitheUum presents a convexity which is more 

 apparent in section (Fig. 33, la). This is the forming fundus of the 

 secondary buccal sulcus, which after the separation of the orbital 

 inclusion, replaces the buccal sulcus as the lateral border of the mouth. 

 The pars cylindrica (fS') is well constricted at its junction with the oral 

 epitheHum and is beginning to undergo a displacement ventrad. This 

 is more clearly to be seen in the sections (Fig. 33). The ventral 

 separating sulcus becomes deeper as the displacement increases. 

 Crairiad it also widens into a shallow concavity in the region of the 

 pars lata (Fig. 32). These sections are disturbed by a tear along the 

 axis of the fold, an artefact which occurs with wearisome iteration in 

 embryos otherwise satisfactorily sectioned, and causes the orbital 

 inclusion to resemble an open fold. It seems to depend upon an as 

 yet imperfect adhesion of the opposed periderm layers. An undam- 

 aged section of a shghtly older embryo is given for comparison in 

 Fig. 42. 



In the 13.5 millimeter embryo (Fig. 34) the changes are slight. The 

 constriction is complete along the greater part of the pars cylindrica ; 

 the separating sulci have met, but the inclusion remains in contact 

 with the oral epithelium and no mesenchyme has entered the cleft. 

 The dorsal separating sulcus, after broadening beside the pars lata, 

 turns laterad and now extends to the buccal sulcus. In consequence, 

 the narrowing fold of the cranial process is depressed ventrad in ref- 

 erence to the buccal sulcus, causing the border of the model in this 

 region to present some resemblance to a knife blade with the edge 

 turned. In the sections from a second embryo of 13.5 milhmeters 

 (Fig. 57) the fold of the cranial process is seen to be fundal in position 

 but deflected rather sharply ventrad. The buccal sulcus has 

 now a well-defined arch ; the pars lata occupies its crown, the pars 

 cylindrica its decUne ; the cranial process extends a short distance 



