2 24 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



THE PAROTID 



The formation of the parotid is foreshadowed in the embryos of 

 1 1. 5 millimeters by minute changes in the buccal sulcus affecting the 

 segment that intervenes between the orbital inclusion and the angulus 

 oris. A small fairly circumscribed area where the nuclei are crowded 

 appears in the mesenchyme below the floor of the maxillomandibular 

 plane close to the buccal sulcus (Fig. 24. /j). It extends from the angu- 

 lus oris to the orbital fold. In the epithehum opposite a change in the 

 position of the nuclei accompanies its appearance. 0^•er a narrow 

 strip bordering upon the buccal sulcus they withdraw towards the oral 

 ends of their cells, leaving a clear zone of cytoplasm ectad. At first 

 sight there seems to be a conca\ity of the ectal surface of the epithehum, 

 but on closer examination the basement membrane may be seen to 

 pass in an even curve to the fundus of the sulcus. The ental surface 

 is convex. This is due to the abrupt tliinning of the epithelium of the 

 sulcus at a point just mesad of the mesenchyme condensation, where a 

 very faint furrow can be observed. 



The embryos of 1 2 millimeters form a small series in which the develop- 

 ment of the parotid may be followed from the stage we have just de- 

 scribed to the formation of its sprout. In the least advanced, No. 100, 

 conditions difTer little from those found in the 11.5 millimeter embryo. 

 The convexity of the floor is somewhat more pronounced, encroaches 

 more upon the lumen, which laterad close to the buccal sulcus is 

 undergoing obliteration (Fig. 46). Here the domed periderm cells of 

 the roof and floor interlock, and a small less deeply staining area forms 

 the axis of a minute flange. The region thus altered is a short seg- 

 ment, about 40-50 /i, of the buccal sulcus, midway between the angulus 

 oris and the orbital inclusion, at the region of the postangular bend. 

 The flange diminishes in both chrections ; its lumen is gradually re- 

 stored and widens into a buccal sulcus of the same general character 

 as in the embryos of 11.5 millimeters. 



In embryo No. 217 (Fig. 47) the convexity entad is larger, but there 

 is as yet but little concavity of the ectal surface of the epithehum. 

 The fundus of the buccal sulcus is sUghtly deflected ventrad. The 

 faint furrow which forms the mesal hmit of the thickened epithehum 

 is deeper. The flange has the same general appearance as in embryo 



