466 EDWARD B. POULTOX. 



posterior region are covered with fine hairlike papilla3 (fig. 8, 

 jT/;, &c.). These are stoutest and longest at the sides, shortest, 

 smallest, and most crowded in the raphe (fig. 1). In a hori- 

 zontal section, taken between the anterior gustatory organs^ 

 I calculated that there are over 500 of these papillse to the 

 square millimetre. This is probably a fair average for the 

 whole surface. 



The roof of the mouth exactly fits this convex part of the 

 tongue, and the former is covered with dense epithelium, 

 presenting minute ridges against which the fine papillae 

 must rub. 



This is the only part of the tongue upon which gustatory 

 areas occur, there being two pairs, an anterior and posterior. 

 The anterior pair (a h o, figs. 1 and 2) are situated on the 

 convex surface behind the horny teeth. All that can be seen 

 from the surface is an oblique furrow, but it is shown by 

 sections that the bottom of this furrow is invaginated upwards 

 into a ridge which bears the taste-bulbs over the whole of its 

 circumference (fig. 8). The lips of the furrow are surrounded by 

 comparatively stout and short papillae, of which the axial up- 

 growths of mucosa are continued from the tissue enclosed between 

 the superficial epithelium and its prolongation downwards to 

 form the furrow. The inner walls of the furrow are formed of 

 corneous cells continued from the papillso encircling the 

 opening. This corneous layer ceases below where the furrow 

 becomes expanded to contain the ridge. One of the most 

 interesting things about this whole organ is that the furrow 

 can almost certainly be closed by the contraction of smooth 

 muscle-fibres arranged as a sphincter. Smooth muscle-fibres 

 are very difficult to identify with certainty in a section, but I 

 have no doubt of their presence and arrangement. So effective 

 is this closure that I have been entirely unable to detect a sign 

 of the organ in some specimens, by examination of the surface 

 with a lens. Of course the stout papilla) would meet during 

 approximation of the lips, and act very effectively in prevent- 

 ing the entrance of particles. Smooth muscle-fibres are pro- 

 bably present in the posterior organs, but they cannot be nearly 



