250 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



postangular bend. This is but a short distance craniad of the orbital 

 angle where the orbital fold is still advancing ; the sagittal segment of 

 the buccal sulcus is extremely short, and the interval between the 

 two folds, which are as yet incomplete, is correspondingly minute and 

 tends to be encroached upon by the folds. Nevertheless, in the less- 

 developed embryos of this stage (Nos. 100, 107, 217) it is present, and 

 has a length varying between 27 and 50 /i. Here the sulcus, while 

 presenting in section a high degree of angularity of the ental contour 

 of its fundus and an appreciable narrowing of its lumen, is not actually 

 reduced to a fissure, nor is a flange present, until the tapering cranial 

 process of the inclusion is reached. In embryo No. 78 the parotid on 

 the right side is a flange 100 m in length, increasing to a maximum and 

 as gradually diminishing in breadth ; a minute fissure indents its base 

 which, deepening and widening craniad and caudad, reduces the flange 

 and restores the lumen of the buccal sulcus. An interval of 60 /* 

 separates the flange from the orbital inclusion. On the left side the 

 parotid has the same structure, with the difference that caudad the 

 flange, while reduced in width, is not wholly lost, but extends into con- 

 tinuity with the orbital inclusion. Here we have an early example of 

 what has been termed the orbitoparotid bridge, a condition occurring 

 as an unusual variant in embryos between 1 2 milhmeters and 15.5 milh- 

 meters in length (Fig. 44). In embryo No. 263, the most advanced of 

 the embryos rated at 1 2 milhmeters, a similar bridge is present on both 

 sides. These embryos, as has been pointed out, form a small series 

 illustrative of the early condition of the parotid and consequently of 

 the orbitoparotid interval. In the less advanced (Nos. 100, 107, 

 217) the interval is present; its absence in the older embryos (Nos. 

 78 one side, and 263) is, then, a secondary condition due to the extension 

 of the folds at a rate exceeding that of growth in the sagittal segments 

 of the buccal sulcus. The primitive independence of the parotid is 

 further shown by the shape of its flange, which, broadening to a maxi- 

 mum, undergoes a decHne towards the interval, so that even in cases 

 where this is bridged and the parotid is continuous with the orbital 

 inclusion, it cannot be interpreted as a simple extension of the latter 

 fold, but appears distinctly as an added or annexed element. The or- 

 bitoparotid interval is, therefore, a residuum of unfolded sulcus, tend- 

 ing from the first to be encroached upon by its limiting folds, and regu- 



