8 DR. C. F. SONNTAG ON THE ANATOMY 



between them are not raised above the general surface. Behind 

 these the ridges appear and increase both in length and pro- 

 minence till a point is reached almost level with the outermost 

 vallate papilla of the corresponding lateral row. After that they 

 diminish in size, but increase in prominence till the posterior 

 limit of the organ is reached. Many ridges ai'e simple, but a 

 few are divided by small secondary sulci. 



Ridges pass across the dorsum from the upper ends of the 

 ridges of the lateral organs. These either encircle the vallate 

 papilla? or pass backwards on their outer side. 



The Inferior Surface (text-fig. 1 C &, 1 B, I). 



The inferior surface presents for examination a mesial sulcus, 

 two plicae fimbriatae, the papillary border, frenum and sublingual 

 fold, or frenal lamella, so called by Pocock (text-fig. 1 B, k, & 

 1 C, e). 



The mesial sulcus (text-fig. 1 0, a) extends backwards from 

 the posterior border of the papillary zone to the attachment of 

 the frenum. It is not occupied b}>- any crest as in the Gorilla. 



The plicce fimbriates (text-fig. 1 0, c) are, it is acknowledged, 

 remnants of the sublingua of the Prosimia?, and in one of my 

 specimens the two plica? and intervening piece of nrucous mem- 

 brane have the appearance of an under tongue. 



The plicae are two longitudinal folds, almost touching in front, 

 running backwards and outwards from near the apex to a point 

 well behind the middle of the tongue, but in one of my specimens 

 they are nearly parallel to one another. They lie on the lateral 

 aspects of the inferior surface between the mesial sulcus and the 

 edges of the tongue. Each one has undulating and crenated 

 edges, and increases in width from before backwards. 



When a vertical section of the tongue is made about its centre 

 (text-fig. 1 D) one sees the mucosa of the floor of the mouth (d) 

 reflected to form the frenal lamella (c). From the upper surface 

 of the latter it is reflected on to the plica (b), and thence to the 

 under surface of the tongue (a). The mucosa between the 

 plica fimbriatae and the sublingual fold is thrown into many 

 small folds. 



The Sublingual Fold (text-fig. 1 C, e). 



The sublingual fold, or frenal lamella (Pocock), lodges 

 Wharton's Ducts. It is triangular in shape with the base 

 behind. The apex is bifid and the two ducts open on the points 

 which are very sharp ; the edges are undulating and crenated. 

 Its mucosa is continuous with that of the floor of the mouth 

 below and the frenum lingua? above. 



Some have said that the sublingual fold corresponds to the 

 sublingua of the Prosimiae, but most anatomists are agreed that 

 the plicae fimbriatae represent it, so the tongue of the Chimpanzee, 

 which possesses both, is sufficient to disprove the statements of 

 the former group of observers. 



