TONGQE OF ORNITHORHYNCHUS PARADOXUS. 455 



upper surface it turns suddenly forwards and is lost. There is 

 a groove in front of the fold and overshadowed by it. This fold 

 may be considered as the posterior limit of the whole tongue. 

 The fold and groove, the pit, and the whole of the upper sur- 

 face of the posterior division, appear quite smooth (although 

 really papillate for the most part), while the lateral surfaces 

 and the anterior overhanging surface appear rough from the 

 presence of small and generally hair-like papillae. Just behind 

 the teeth are two deep grooves (figs. 1 and 2, a 5 o), directed 

 obliquely to the long axis of the organ. These contain the 

 structures which bear the taste-bulbs, but the former cannot 

 be seen from the surface. There is also another gustatory 

 structure in each groove in front of the fold (figs. 1 and 2, 

 ph 0.), but in this case the convex surface which bears the 

 bulbs can be seen. I have omitted to give dimensions in this 

 general description because the size of the parts described is 

 given in figures 1 and 2. 



Histological Account of the Tongue. — For the pur- 

 poses of this description it is convenient to divide the organ 

 into an anterior and posterior part; but the former in this case 

 should include the anterior surface of the posterior part and 

 the horny teeth. These two regions are histologically very dis- 

 tinct. The anterior region (1) contains exclusively tactile and 

 mechanical papillae, while the posterior region (2) bears the 

 gustatory structures, together with papillae of probably me- 

 chanical function, and different in structure from many of those 

 on the anterior region. 



1. The Anterior Region. — The upper surface of the tongue 

 at the tip (and for about 19 mm. behind the tip in the middle 

 line, and rather more at the sides) is covered by large papillae 

 (fig. 1), and presents many points of difference from the surface 

 of the more posterior parts. This region is, therefore, conve- 

 niently subdivided into (a) an anterior subregion of large 

 papillae (easily recognisable in fig. 1) and (b) a posterior sub- 

 region of small papillae (including the horny teeth). 



A. The Anterior Subregion. — The papillae, which form 

 an irregular fringe (one or two deep) on the sides and front of 



