DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 267 



made. Clearly it is close to the junction of the two sulci and as the 

 interval between it and the parotid sprouts may produce as variants 

 orbitoparotid elements, it is apparent that we are deahng with a 

 series of glands in process of separation into parotid and orbital groups, 

 and that the interval in the cat is not yet absolute. The point of prime 

 importance in the site of the first orbital is its entomasseteric posi- 

 tion, as contrasted with the jiromasseteric situation of the parotid 

 and orbitoparotids, which evidently determines its direction of growth 

 along the only path permitted, caudad and dorsad into the orbit. As 

 further the border of the masseter advances slightly relative to the 

 buccal sulcus during development, the time of the appearance of a 

 sprout has some influence in determining its direction of growth, those of 

 late appearance having less chance of escaping the embrace of the 

 muscle. As the glandiferous activity of the marginal cavity, in con- 

 trast to that of the alveolingual region, is accelerated craniad and 

 later extends to its caudal portion, it is evident that early appearance 

 and cranial position here cooperate to achieve an ectomasseteric po- 

 sition for some of the elements, wliile later estabhshment and coincident 

 caudal site determine the selection of the orbital path, the masseter in 

 each case being the chief factor in determining the topography of the 

 glands, as by its apposition to the oral epithehum it is responsible for 

 the sterile, or nearly sterile, interval between the analges of the parotid 

 and orbital elements of the buccal sulcus series. 



The direction of least resistance for the growth of an entomasseteric 

 sprout is already strictly determined by the relations of adjacent parts. 

 Dorsad is a dense mesenchyme condensation, horizontally placed and 

 by its mesal border coming into close relation to the oral epithe- 

 lium, the anlage of the alveolar process and maxillary tuberosity ; 

 laterad is the deep facial vein ascending into the orbit under cover 

 of the masseter and the anlage of the zygomatic arch (Fig. 102, 515). 

 The interval between these structures and the buccal sulcus is filled 

 with loose mesenchyme which, caudal to the alveolar process, is widely 

 continuous with that of the orbit, to reach which the sprout of the first 

 orbital must extend itself a relatively considerable distance caudad, 

 before it may turn dorsad and find room to expand. 



In the 21 millimeter embryo the orbital has lengthened to a short 

 crest along the dorsal wall of the buccal sulcus, and now extends 



