58 



pus) didactylus), and in that species or subgenus exclusively ; the carpal bones being 

 seven, and the reduction to that number resulting, also, from the connation of the 

 scaphoid and trapezium. A scapho-trapezial bone exists in the Ai or Three-toed Sloth 

 (Bradypus (Acheus) tridactylus), but the carpus is further reduced in this species or 

 subgenus to six bones by the confluence of the trapezoides with the os magnum. The 

 trapezius is a distinct ossicle in the Chlamyphorus, as in most other Armadillos ; in the 

 Basypus sex-cinctus it coalesces with the trapezoides. In the Pangolins (Manis) the 

 scaphoid coalesces with the lunare, not with the, trapezium. In the true Anteaters 

 (Myrmecophaga), and in Orycteropus, the ordinary eight carpal bones retain their indi- 

 viduality. 



Digital Phalanges. — The stunted metacarpal of the pollex, in the Megatherium, bore 

 no rudiment of a digit. They were powerfully developed and unguiculate in the three 

 following digits. 



The index digit (Plate XXI., n) has three phalanges: the proximal one (1) is almost 

 twice as broad, and more than twice as deep, as it is long ; the metacarpal surface pre- 

 sents a deep and wide, vertically elongated, subangular concavity, fitting the vertical pro- 

 minence and lateral facets of the distal joint of the metacarpal ; the distal surface of the 

 proximal phalanx presents a vertical angular fissure dividing two oblong convexities. 

 The mid-phalanx (ib. H, ») has a proximal trochlea playing on the preceding, the median 

 vertical ridge being overhung by the produced upper rough surface ; the distal articula- 

 tion repeats that of the proximal phalanx, but the median fissure is less deep, and the 

 lateral convexities are more regularly rounded and prominent. The ungual phalanx 

 (ib. n, 3) exceeds the length of both preceding phalanges ; the upper or dorsal side of 

 its base is produced backwards into an obtuse point; the rough sheath of the claw 

 extends along three-fourths of the phalanx ; it is convex radiad, vertical and flat ulnad ; 

 the core presents a rough edge radiad and a vertical rough surface ulnad, and is smooth 

 and convex transversely at its base, both above and below. 



The proximal and middle phalanges of the digitus medius (ib. in, 1...2) are confluent, 

 the line of anchylosis being indicated by a vertical ridge along both the inner and the 

 outer sides, and by a curved ridge convex backwards on the upper or dorsal side. The 

 proximal articular surface presents a deep vertical channel, with a narrow elongated 

 subconcave surface continued from its radial side, and a still narrower flat surface from 

 the opposite side. The distal articular surface of the composite bone has a deep median 

 vertical groove dividing two convexities. The compound phalanx presents two rough 

 tuberosities below, one terminating each bank of the vertical articular proximal channel ; 

 there is a smooth depression above, and another below, close to the distal trochlea. The 

 enormous distal phalanx (ib. in, a), of twice the vertical breadth of the adjoining claw 

 phalanges, is very little longer than that of the second digit ; it is flattest on the ulnar 

 side, to which the upper convexity slightly inclines. The base or palmar part of the 

 phalanx is the broadest, is convex both lengthwise and transversely, and is perforated 

 by two canals, for the large vessels and nerves supplying the claw-core. The surface, 



