HISTOBY OP THE EDENTATA 593 



The name Edentata (toothless) is not very happily chosen, 

 for only the anteaters are quite toothless. Almost all the 

 genera have no teeth in the front of the mouth and the teeth are 

 nearly always aUke, so that the distinction of regions among 

 them is entirely a matter of position in the jaws. In the tree- 

 sloths and many fground-sloths the foremost tooth in each 

 jaw is a more or less enlarged, canine-like tusk. The teeth are 

 always rootless, growing from permanent pulps, and are without 

 enamel, made up of dentine, which is sometimes homoge- 

 neous and sometimes in layers of different hardness, and with 

 a covering of cement, usually thin and film-like. The number 

 of teeth varies from f to {^ or more, and their form usually 

 approximates a simple cylinder, worn off fiat at the end, 

 though the ends may be bevelled or grooved, differences which 

 are in no way due to pattern but simply to the mode of wear. 

 In the fglyptodonts the teeth were divided by deep vertical 

 grooves into two or three pillars, connected by narrow necks. 

 In most of the edentates there is no change of teeth, the 

 milk-dentition having been completely suppressed, but in the 

 9-Banded Armadillo (Tatu) each of the permanent teeth is pre- 

 ceded by a two-rooted milk-tooth, and some other armadillos 

 have milk-teeth. 



The skull varies much in form and proportions, according 

 to the character of the food and method of feeding. The tree- 

 sloths and tground-sloths have short, roimded heads ; in the 

 fglyptodonts, the skull was short and remarkably deep verti- 

 cally ; while the armadillos have long, shallow heads, with 

 tapering muzzle, the length atid slenderness of which differ in 

 the various genera. In the anteaters the skull is extraordinarily 

 elongate and slender. The sagittal crest is seldom present at 

 all and never prominent. The zygomatic arch may be com- 

 plete or interrupted ; in the tree-sloths, fground-sloths, fglypto- 

 donts and some extinct armadillos, there is a descending, plate- 

 like process given off beneath the eye. 



The backbone displays some ■ of the most remarkable 



2q 



