DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT ' 203 



(Fig. 10, 6). In this section the ectoptilatine sulcus is present as a 

 minute indentation of the oral epithelium dorsally near the base of the 

 fold, which, thus occup>ing the region between the ectopalatine and 

 the buccal sulcus, is seen to be the reduced equivalent of the maxillo- 

 mandibular plane. Craniad the fold disappears and is replaced by 

 a considerable cleftlike space of horizontal direction, extending in 

 the sections (Fig. 9) from the faintly indicated palatomandibular 

 plane to the angulus oris. At this period, therefore, the orbital inclu- 

 sion would appear to correspond to the caudal portion of the plane in 

 its entirety. This holds true in later stages of the caudal portion of the 

 inclusion only, as is shown by the termination of the ectopalatine 

 sulcus at the tip of the inclusion, or in line with it, as has already been 

 stated (Figs. 35, 97). As the maxillomandibular cavity enlarges, 

 the orbital fold is formed at the expense of only its lateral portion, the 

 triangular caudal portion of which is inserted between the orbital fold 

 and the ectopalatine sulcus (Fig. 35). With reference, therefore, to 

 the orbital inclusion, the maxillomandibular plane falls into two seg- 

 ments, a cranial and a caudal, the latter characterized by a reduction 

 of its lateral portion to form the fold. In situation tliis segment is 

 entomasseteric ; the cranial, unfolded region, which escapes the em- 

 brace of the muscle, is promasseteric (compare Fig. 36 with Figs. 37 

 and 38) . The junction of these regions coincides with a change in direc- 

 tion of the buccal sulcus (Fig. 35, 7), which here passes by a gradual 

 curve from a more transverse to a more sagittal course. The curve 

 has been termed the orbital angle. It lies ental to the masseter, where 

 the buccomasseteric nerve crosses the buccal sulcus (Fig. 35, 6y). 



It has already been stated that the lateral portion of the mouth in 

 the 8.5 millimeter embryo is lined with thickened epithelium, extending 

 mesad to regions corresponding to the ectopalatine and lingual sulci. 

 This area corresponds to the whole of the maxillomandibular and the 

 ventral epthelium of the palatomandibular plane and alveolingual region. 

 Out of this epitheUum the several anlages of the dental ridges and 

 salivary glands emerge as local retentions and increases of the thicken- 

 ing, which in intervening regions undergoes relative attenuation. A 

 thinning first appears in the alveoHngual fold, wliile mesad along the 

 lingual sulcus, a very narrow strip of thicker epithelium persists. The 

 inferior dental anlage is distinguishable at 11.5 miUimeters as a wide 



