2 54 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



In a very small minority of cases the folds are continuous and the 

 interval is effaced by an orbitoparotid bridge. This has already been 

 described in the 12 millimeter embryos. It was found complete but 

 five times in our material ; the oldest embryo in which it was retained 

 intact was 15.5 miUimeters in length. In embryo No. 127 an almost 

 complete bridge is interrupted close to the parotid by a small incisure 

 (Fig. 43). Cases in which the lumen of the buccal sulcus is reduced 

 in the whole extent of the interval, but without the formation of a 

 flange, are more frequent. In these the lumen is fissurehke, the fun- 

 dus markedly acute, and frequently deflected ventrad (Fig. 56). For 

 the rest there is regularly a marked angularity of the fundus of the 

 sulcus over part or the whole of this segment, suggesting a ten- 

 dency to a fold. In length, in the degree of folding, in the presence 

 of incomplete keels, and the formation of sprouts, the intervals vary 

 widely and are frequently asymmetrical. In this respect almost 

 every embryo has an individuality of its own. 



While the two folds of the buccal sulcus, the orbital and the parotid, 

 are from their inception separate and only rarely become continuous, 

 there is yet evidence to show that this independence has been derived 

 from a more primitive condition, where a continuous fold involved the 

 cranial as well as the caudal segment of the buccal sulcus. The slen- 

 der rodlike condensation of the mesenchyme ventral to the floor of 

 the ma.\illomandibular plane, extends in embryos of 12 millimeters 

 from the angulus oris to the orbital angle. Corresponding to it the 

 epithelium of the floor is elevated to form a ridge parallel to the buccal 

 sulcus, which extends to the postangular bend, usually not quite to 

 the border of the masseter. The condensation in the mesenchyme 

 gradually becomes indistinct and is lost, but can in the majority of 

 embryos of 14-15 millimeters still be recognized between the parotid 

 flange and the cranial process of the inclusion ; occasionally it persists 

 in a part of its course in embryos of 17-18 millimeters. In the cases 

 where an orbitoparotid bridge was formed the condensation was well 

 marked. There is further a continuous epithelial thickening along 

 the fundus of the buccal sulcus in its whole extent. This becomes in- 

 corporated in the folds of the parotid and of the orbital inclusion. 

 In the interval it is gradually thinned, but is not wholly lost until 

 after the separation of the cranial process. 



