THE ALIMENTARY CANAL AND ITS APPENDAGES 161 



teeth arise in relation to epithelial papillae, which project above 

 the surface of the mucous membrane of the mouth. A tract of the 

 epithelium of the jaw subsequently sinks down into the meso- 

 dermal tissues to form the so-called dental ridge, from which the 

 actual teeth then develop. The dental ridge of the higher Verte- 

 brates commences to form very early, long before the first appear- 

 ance of the bones. In this early formation of the dental ridge 

 the phylogenetic early appearance of teeth is ontogenetically re- 

 capitulated. The occurrence of freely projecting papillae prior to 

 the formation of the dental ridges seems to have been lost in 

 most Mammals, through abbreviation of the embryonic stages. 

 Eose has, however, lately proved the existence, in Man, of 

 temporary traces of papillae at a period antecedent to the sinking 

 down of the dental ridge. 



THE SUBLINGUA 



Gegenbaur has devoted special attention to a system of folds 

 on the under surface of the tongue (plica fimbriata), which are 

 very distinctly developed in children at and soon after birth, but 

 in adults are found only in various stages of reduction. 



In its general form this organ resembles the sublingua of 

 the Prosimii, in which animals it attains its most independent 

 development in the Slender Loris (Stenops) of Ceylon. It is in 

 this creature supported by cartilaginous, fatty, and connective tissue, 

 its investing epithelium being raised into papillae and showing 

 a tendency to become horny. In the allied Tarsius and in Lemur 

 degeneration has obviously taken place ; since, in the latter, the 

 cartilaginous supporting tissue has altogether disappeared and the 

 organ is no longer independent, so far as its relations with 

 the tongue are concerned. The sublingua would thus appear to 

 have formerly possessed a well-developed supporting skeleton, 

 inherited from the lower classes of animals, and we are, in fact, 

 reminded of the rod-like process of the basihyal which, in Lizards 

 and some Chelonians, passes so conspicuously into the base of the 

 tongue. Thus considered, the sublingua may be regarded as the 

 morphological equivalent of the tongue of the lower Vertebrata, 

 and the actual Mammalian tongue would appear to have been 

 to a certain degree acquired [within the limits of the Mammalian 

 phylum]. The tongue and sublingua thus appear to be organs 

 of very different phylogenetic significance, and there is some 

 reason for thinking that the muscular tongue has probably 



