ANATOMY OF THE THREE-TOED SLOTH. 159 



bears a small tubercle in the mid-line at a distance of 1 mm. 

 from the free edge (Plate I. B). There is, however, no uvula, as 

 was pointed out by Rapp (10). 



The Teeth. 



The teetl) have been fully described in their structural and 

 developmental aspects by Rapp (10), Senion (11)? and others, and 

 I I i.ive nothing to add to their accounts. 



The Tongue (text-fig. 10). 



Rapp (10) has given some scanty details of the tongue, so a 

 detailed description is required. 



My fresh specimen has the following measurements : — Length 

 from the apex to the epiglottis, 3 - 85 cm. ; length of the oral part, 

 2-89 cm. ; length of the pharyngeal part, "96 cm. ; greatest width 

 (i. e. between the lingual attachments of the anterior faucial 

 pillars), 1*7 cm. : width of the apex", 7 cm.; thickness in the 

 vallate papillary region, 1-25 cm.; thickness at a point T4 cm. 

 posterior to the apex, 11 cm.; thickness of the apex, '4 cm. 



The tongue is, therefore, short, narrow, and. thick. Its width 

 first decreases rapidly, but later maintains a constant dimension 

 to the apex. The thickness remains almost uniform, on the 

 other hand, in the posterior two-thirds and then rapidly decreases 

 towards the apex. 



The apex has a fine mesial notch, and is covered with small 

 conical and large flat fungiform papilla?. There is a faint mesial 

 sulcus which, however, is irregular, and the lens shows how it is 

 replaced in parts by fungiform papilla?. ; the latter are, however, 

 invisible to the naked eye. The lateral borders are massive, and 

 have a single row of large fungiform papillae ; they also possess 

 vertical rows of conical papilla? with backwardly-directed points. 

 No lateral organs are present, as shown by Gmelin (13). 



The two circumvattate papilla lie side by side, and both are 

 circular and polished. When the tongue is fresh their free sur- 

 faces are flush with the surface of the tongue. When, however, 

 it is placed in preserving fluid the papilla? are retracted within 

 their fossae, thus demonstrating an action similar to what occurs 

 in Monotremes and some Marsupials. The Valiums are promi- 

 nent, granular, and surrounded by conical papillae. Mayer (14) 

 saw three papillae. 



The fungiform papilla} are large, flat, and not numerous. They 

 have the usual arrangement in clusters and rows of varying 

 degrees of obliquity which characterises the Mammalian tongue. 

 They extend from the apex back beyond the vallate papilla?, but 

 they stop short of the zone of lymphoid tissue on the base. They 

 form a single row on the lateral borders of the tongue, but the 

 papilla? of the row are discrete. 



The conical papilla 1 are all filiform and possess one or more 

 points; those in the mid-line have their points directed back- 

 wards, but those at the sides look backwards and inwards, They 



