200 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



alveololingual sulcus. As it is by no' means a furrow comparable to 

 the others in the oral cavity, but a broad gutter, it seems justifiable 

 to alter the term. 



The circumlingual region has the shape of an inverted U, and pre- 

 sents three planes or segments, which, named by their boundaries, 

 are the craniolingual, and the paired palatolingual planes. The 

 cranioKngual plane is horizontal in the sections (Figs, ig-20) or 

 nearly so (Fig. 22); in reconstruction it has a gentle sagittal curve 

 with dorsal convexity. It is bounded by the dorsum of the 

 tongue and the basis cranii with the adjacent mesenchyme. Laterad 

 its roof joins the palate process at an angle (the entopalatine angle) 

 which is continued craniad into the nasal sulcus (Fig. 23), and caudad, 

 becoming rounded, is continuous with the tubotympanic sulcus. At 

 the attachment of the hypophysis the craniolingual plane joins the 

 pharynx almost at right angles. The palatolingual planes have a 

 ventrolateral inchnation in embryos of 11. 5 millimeters (Figs. 13, 14). 

 Gradually they become vertical (Figs. 16, 36-38), and in the embryo 

 of 13.5 millimeters the primitive direction is retained only in their 

 caudal portion (Fig. 39). Later they acquire a ventromedian slope 

 and the palate processes come to embrace the tongue more closely 

 (Fig. 100). 



The alvcolingual regions have the shape of broad horizontal gutters 

 diverging from the frenulum, where they are confluent, to the region 

 of the first entodermal pouch, where, becoming narrow, they are con- 

 tinuous with the lateral borders of the phar>-nx. Against the tongue 

 the region is defined by an angle (Fig. 14) which gradually deepens 

 to form a furrow, (29) the sulcus lingualis. In the cat the sulcus 

 appears in separate segments, one beside the tip of the tongue (Fig. 15), 

 a second later portion caudad in the neighborhood of the Ungual nerve 

 and its large ganglion (Fig. 16). The two segments are usually con- 

 tinuous in embryos of 13.5 millimeters and over. Occasionally 

 union fails to occur ; quite regularly this intermediate portion is 

 shallower than the earlier formed segments of the sulcus. 



In the cat the alveolingual region passes laterad into direct conti- 

 nuity with the marginal cavity ; the alveolar sulcus, which forms a 

 conspicuous boundary in man (cf. Part II, Figs. 12-17), is here indefi- 

 nite or lacking altogether. 



