90 EDENTATA order v 



either complete or interrupted, sometimes even rudimentary. It is dis- 

 tinguished, in the Gravigrada, Tardigrada and Glyptodontia, by a long 

 process directed downward, and another less strongly developed one which 

 is directed upward aud backward. 



Almost all edentates are monophyodont. Since milk - teeth precede 

 the permanent dentition in the genera Tatusia and Oryderopus, it may be 

 concluded that the ancestors of the Edentata were diphyodonts. The molars 

 of the upper and lower jaws are similar or but slightly difterentiated. They 

 number from 4 to 10, sometimes even more. They are composed of dentine 

 and an outer layer of cement. The dentine of the tooth consists, as a rule, 

 of layers of varying hardness and different composition. The outer and 

 hardest layer, traversed only by very fine dentine canals, surrounds a central 

 vasodentine core, perforated by many coarse canals. The cheek teeth 

 of Edentata are prismatic in form and attain frequently to a considerable 

 height. They are without roots and open below, growing continually as 

 their crowns are worn down. These last are most often worn down evenly, 

 seldom obliquely ; or transverse or oblique ridges may be formed. Not 

 infrequently a part or all of the teeth possess on the outer or inner side, 

 or on both, vertical furrows, which constrict the tooth and in the Glyptodonts 

 convert it into a series of pillars connected by two or three narrow bridges. 



The fore- and hind-limbs are sometimes equally well developed, but 

 in general the hind -limbs are much more robust than the fore, and in the 

 Glyptodonts much longer as well. The high median crest of the scapula 

 terminates in a very long, overhanging acromion, which, in the Gravigrada, 

 even fuses with the unusually well developed coracoid process. Adjoining 

 this crest and slightly distant from the posterior surface of the scapula 

 is a second, rather weak crest. Only the Gravigrada and a few armadillos 

 possess a clavicle. 



The humerus almost always has an entepicondylar foramen and a very 

 well developed deltoid crest. Radius and ulna remain separate. The carpus 

 has a centrale only in Manis, and consists usually of seven separate carpal 

 bones and one pisiforme. Not infrequently there is a fusion of the magnum 

 and trapezoid, or of the scaphoid and lunar, or in other cases the trapeziiim 

 fuses with the scaphoid or the first metacarpal. In some cases all of the 

 metacarpals are developed, or again, only four, and very seldom but three 

 are functional. The digits are of varying lengths, five to three bearing 

 phalanges, of which the terminal ones are developed as narrow, long, 

 compressed and usually sharp claws. 



The pelvis of the sloth and Gravigrada is wide anteriorly, but narrow 

 and elongated in all other edentates. Except in Ori/derojnis, the unusually 

 well developed ischia are joined with the caudal prolongation of the sacrum. 

 The pubic bones are long and slender, the symphysis short, the obturator 

 foramen large. The tibia and fibula are in some cases separate, in others 

 they become fused distally or at both ends. 



The tarsus and hind-limb of Oryderopus, a.nt-eateTS and armadillos are usually 

 pentadactyl ; in the remaining forms the outer and inner metatarsals are 

 frequently degenerate. The calcaneum has an elongated, rough tuber, the 

 astragalus a concave trochlea for the articulation of the tibia, and on the outer 

 surface a groove for the conical process of the fibula. The first and second 

 phalanges are short, at times fused or united with one of the meta- 



