248 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



in a portion of the duct in embryos of 31 millimeters. In the 34 milli- 

 meter embryo it extends from the orifice into the primary branches. 

 In this embryo the lumen is continued to the surface of the oral epithe- 

 lium by a channel, among the cells of the stratum corneum, but lack- 

 ing an intrinsic wall. It is difficult to see how such a passage should 

 form save under the influence of the liow of fluid. As the epithelium 

 of the gland shows no histogenetic changes and its buds are solid, the 

 only obvious source of such a fluid is the Hquefaction of the central cells. 



THE ORBITOPAROTID INTERVAL AND ITS DERIVATIVES 



Between the parotid anlage and the orbital inclusion a segment of 

 the buccal sulcus more or less completely escapes inclusion in the folds 

 of these anlages; this is the orbitoparotid interval (Fig. 163, 75). 

 With the separation of the orbital inclusion its caudal boundary is 

 lost. It is desirable, however, in view of variant sprouts which appear 

 in the course of the buccal sulcus, to distinguish between the region 

 where the sulcus is obliterated to form the inclusion, and the portion 

 which escapes folding ; in other words, between the secondary buccal 

 sulcus and the orbitoparotid interval. The late embryonic and adult 

 conditions of the furrows (Fig. 165), when the secondary buccal (la) 

 is directly continuous with the alveobuccal sulcus (25) without point 

 of demarcation, and further the obliteration of the greater part of the 

 buccal sulcus in the remodeling of the vestibule, efface the early land- 

 marks, and render impossible an exact determination of the caudal 

 limit of the interval. The sprout of the first orbital gland, which ap- 

 pears shortly after the separation of the cranial process of the inclusion, 

 which, for reasons to be given later, is with a high degree of probability 

 to be assigned to the secondary buccal sulcus, is yet so near the cranial 

 extremity of that furrow as to make it possible that it is itself a deriva- 

 tive of the orbitoparotid interval. In these circumstances the error 

 in taking it as the approximate caudal limit of the interval is small. 

 The interval becomes, therefore, in stages subsequent to the separa- 

 tion of the inclusion, the sagittal distance between the parotid and the 

 first orbital sprout. Still later the orbital sprout advances by the 

 formation and constriction of a keel at the expense of, and encroaching 

 upon, the interval ; its duct comes to have a proximal segment of 



