454 EDWARD B. POULTON. 



the organ are shown in figures 1 and 2, which are drawn of the 

 natural size. There is an obvious division into an anterior and 

 a raised posterior part. 



The Anterior Division is only free from the floor of the 

 mouth for about one third of its own length, and therefore the 

 movements of the tongue must be very limited. 



The upper surface is covered anteriorly with large papillae 

 directed backwards, becoming gradually smaller posteriorly, 

 where little more than a rough appearance can be detected by 

 the naked eye. The sides and lower surface of the free part 

 are perfectly smooth, and the large papillae terminate abruptly 

 at the lateral and anterior limits of the upper surface. Poste- 

 riorly, however, the smaller papillae are continuous on to the 

 sides of the organ, and appear to be present upon the mucous 

 membrane of the floor of the mouth. There is no trace of a 

 raphe in the anterior part. 



Posterior Division. — The anterior surface of this division 

 is continuous with the upper surface of the anterior division, and 

 the former overhangs the latter, making with it an angle of 60° 

 (fig. 2). This surface is 11 mm. broad where it joins the an- 

 terior division, and above this its lateral contours slope upwards, 

 forwards, and inwards, to the most anterior part of the posterior 

 division. Here the superior and anterior surfaces are continu- 

 ous, and at this point are two large horny papillae or teeth 

 (deserving this latter name as much as the maxillary teeth of 

 Ornithorhynchus, which are also epithelial). 



The internal sides of the teeth slope inwards, and appear to 

 be continuous ; the apices are broad and chisel-like. The bases 

 are surrounded by small hair-like papillae, which spring from 

 the teeth themselves. Posteriorly the upper surface presents a 

 small and shallow pit in the middle line, and from the anterior 

 margin of the pit a linear raphe is continued for a short dis- 

 tance, disappearing as a slightly -marked groove. A fold is 

 formed at the junction of the mucous membrane of the floor of 

 the mouth with the side of the posterior part of the tongue. 

 This fold first appears at about the middle of the side, and runs 

 backwards and upwards, and on nearly reaching the pit on the 



