THE ALIMENTARY CANAL AND ITS APPENDAGES 161 
teeth arise in relation to epithelial papille, 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 papille prior to 
the formation of the dental ridges seems to have been lost in 
most Mammals, through abbreviation of the embryonic stages. 
Rose has, however, lately proved the existence, in Man, of 
temporary traces of papille 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 papille and showing 
a tendency to become horny. In the allied Zarsiws 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 hmits 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 
M 
