DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 305 



3. From the buccal sulcus are formed the orbital inclusion, the 

 parotid, and inconstant orbitoparotid elements. 



The orbital inclusion is a fold extending craniad from the plane of 

 the mandibular nerve, and reaching the angulus oris in embryos of 

 10.5 milhmeters; with the lengthening of the buccal sulcus it becomes 

 relatively displaced caudad and assumes an entomasseteric position. 

 The first formed portion is cylindrical, pars cylindrica ; at the orbital 

 angle it broadens, pars lata, and is thence continued forward as a 

 variable tapering cranial process. This rarely extends as far as the 

 border of the masseter, but exceptionally may be prolonged as an 

 orbitoparotid bridge to the parotid (Fig. 164). The inclusion be- 

 comes constricted at its attachment to the oral epithelium, from which 

 it separates first at the junction of the pars lata and the pars cyhn- 

 drica, while its extremities remain longer attached. It finally under- 

 goes displacement laterad towards the quintus muscles. At the 

 orbital angle the pars lata is in contact with the buccomasseteric nerve, 

 a relation which the inclusion permanently retains. Lateral to 

 the nerve a variable lateral process is developed. There are evidences 

 of independent growth in the inclusion, in the presence of sprouts in 

 its cylindrical portion in the 70 millimeter embryo, less certainly, 

 also, at its caudal extremity and in the lateral process (Fig. 165). 



The parotid appears as a minute fold, separate from the orbital 

 inclusion at its inception, but at times becoming secondarily continuous 

 with it (Figs. 163, 164) through an orbitoparotid bridge. The "fold 

 is reduced to a flange, which assumes a triangular shape. At its 

 free angle a process of proliferation is initiated, which extends distad 

 as a sprout below the border of the masseter, and also advances proxi- 

 mad along the free border of the flange and ultimately along the oral 

 epithehum in front of the flange, forming a keel, which becomes con- 

 stricted and freed and ultimately produces the promasseteric portion 

 of the parotid duct. The sprout gives rise to the remainder of the 

 duct system and the epithelium of the gland. Primarily inframuscu- 

 lar, the duct secondarily acquires a transmuscular position. The 

 attachment of the anlage to the oral epithelium is at first fundal, 

 but later becomes dorsal parietal, the buccal sulcus forming a new 

 fundus (subparotid furrow) ventral to the anlage (Fig. 164). 



The orbitoparotid elements are sprouts formed in the orbitoparotid 



