256 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



orbitoparotid interval is established in embryos of 12-13 millimeters. 

 At this period the parotid fold is estabhshed, and the orbital fold is 

 still confined to the region of the orbital angle. The sagittal segment 

 of the sulcus now lengthens, but the muscle maintains its relative 

 position. The orbital fold continues to advance, diminishing in 

 breadth towards the border of the muscle, where in the large majority 

 of cases the process comes to a stop, and the orbitoparotid interval 

 gives rise to no fold. In the embryos of our series of the period of 

 16.5 to 19 millimeters, in which the advance of the fold attains its 

 maximum, not one inclusion extended beyond the border of the 

 muscle, and only in a single instance to that point. The factors favor- 

 ing and impeding the extension of the fold over the orbitoparotid 

 interval must be balanced with some nicety, for in many cases an im- 

 perfect bridge is here formed, and the influence of the masse ter suffices 

 only for the ventral deflection of the flange or fold and not its complete 

 suppression. The variations may well depend upon shght differences 

 in the rates of advance of the fold or muscle, which latter may fail to 

 come within acting distance until a flange is already present, in which 

 case it can only deflect it ventrad and slowly cause its reduction, in- 

 stead of primarily inhibiting its formation. As the masseter is a 

 mammalian neomorph, the fold, the development of which it impedes, 

 must be referred to promammahan forms. It is present both in the 

 embryo and adults of the Hzard and turtle as an open, foldhke ex- 

 tension of the oral cavity laterad and dorsad towards the muscles of 

 mastication, with which it establishes intimate relations, while into its 

 roof open the caudal members of the series of superior labial glands. 



THE ORBITOPAROTLD GLANDS 



Orbitoparotids are sprouts derived from the buccal sulcus between 

 the parotid and the orbital inclusion, or in the case of older embryos 

 between the parotid and the first orbital anlage. They are usually 

 of small size and confined to the triangle, bordered mesad by the oral 

 epitheUum, laterad by the parotid, and caudad by the masseter. A 

 very few tend to enlarge beyond these narrow confines, passing toward 

 the lateral or mesal surface of the muscle. Those that do not attain 

 so large a size may yet, within the triangle, manifest a definitive se- 



