OF REPTILES AND BIRDS. 17 



In a section nearer the tip, the transverse muscle is wanting, but there are a few longi- 

 tudinal fibres, which perhaps represent the lingualis muscle of snakes. The epithelium 

 of the upper surface is still more thickened, and its follicles longer than in the region of 

 the transverse muscle, cut 5. 



The epithelium on the flattened or free portion of the tongue, consists, like the epithe- 

 lium on the tip of the tongue of Ancistrodon, of four distinct and quite sharply limited 

 layers, viz. : — 1, a basal row of columnar cells, upon which rests 2, a layer of polygonal 

 cells ; 3, a stratum of cells, considerably flattened ; 4, the corneous layer. The three 

 lower layers correspond to the mucosa of the round part of tongue. 



V. Conclusion. 



There are a few generalizations to be drawn from the preceding observations, but which 

 must be confirmed by further research, before they can be considered definitely estab- 

 lished. This limitation applies to the following remarks. 



The tongue is to be defined as a projection of the floor of the mouth, capable of inde- 

 pendent motion ; with special intrinsic muscles ; free in front ; supported posteriorly by 

 the hydoidean apparatus, from which the principal longitudinal lingual muscles arise. 



The tongue is supplied with three pairs of nerves ; 1, the lingual, a branch of the fifth 

 pair or trigeminal, which runs above the longitudinal hyo-(cerato-)glossal muscles, and is 

 distributed to the tip of the tongue ; 2, the glossopharyngeal, distributed to the mucous 

 membrane at the side of the base of the tongue, (but not supplying any of the muscles); 

 3, the hypoglossal, running to the cerato-glossal muscle, together with which it enters the 

 tongue. 



The tongue is covered by a stratified epithelium, which is thinnest and simplest pos- 

 teriorly, but is thickened towards the tip, where it is further characterized in reptiles 

 birds and mammals, by two peculiarities, 1, the formation of epidermal papillae or fol- 

 licles, which project into the dermis; 2, the presence of enlarged transparent vesicular 

 nuclei, which might at the first glance of a microscopical examination, be readily taken 

 for the sections of vessels or gland ducts. The sense organs connected with the lingual 

 epithelium I have not studied. 



The tongue may be roughly divided into three parts ; 1, the hase, which is supported 

 by the hyoidean apparatus, in snakes withdrawn behind the sheath and under the floor of 

 the mouth, in birds pushed well forward, but not including the free portion supported by 

 the entoglossum ; 2, the middle or movable muscular portion, covered by a stratified epi- 

 thelium, but little differentiated, except when glands are developed, and perhaps at the 

 sides where the glossopharyngeus is distributed ; 3, the tip, upon which the organs of 

 touch and taste are especially developed. These three parts might also be termed, from 

 the nerves, whose distribution respectively predominates in each part, the hypoglossal, 

 glossopharyngeal and lingual areas. The distinction is real, though not very definite, the 

 three regions having no precise boundaries. 



