96 



attached to the nearly flat distal surface of the huge metacarpal, but does not 

 exceed in size the sesamoid which plays upon the convex surface below the 

 phalangeal joint : a very small slightly concave surface on the distal end of the 

 rudimental phalanx indicates the existence of a second, as simple as, but 

 relatively smaller than, that of the fourth finger. In the right fore-foot the 

 distal end of the metacarpal is enlarged and diseased ; the articular surface for 

 the phalanx being destroyed by ulceration. Such a morbid change is far from 

 unhkely to have happened in a part so immediately concerned in the support 

 and progressive motion of the peculiarly bulky Mylodon. 



The sesamoid bones, as the account of the articular surfaces of the meta- 

 carpals and phalanges has already indicated, are numerous and large ; most of 

 them are oblong and trihedral : the contiguous surfaces of the large pair which 

 play upon the distal articulation of the middle metarcarpal bone, form a wide 

 and smooth cavity for the passage of the strong flexor tendon of the second and 

 distal phalanges. Besides the sesamoid bones, three other bones belonging to 

 the Mylodon appear to have been connected with tendons. They are flattened, 

 of a broad irregular oval figure, with rounded margins, moderately and uniformly 

 smooth, but without any articular surface : some parts of the surface present an 

 appearance of decussating straight fibres, as in the detached dermal bones of 

 Saurians. Two of these ossicles, however, form a symmetrical pair ; and I am 

 therefore disposed to regard them as belonging to the fore-paws, and to have 

 been imbedded in the flexor tendons, one in each palm, for the purpose of aug- 

 menting the force of these tendons, as do the analogous bones in the fore-feet 

 of the Armadillos. The third bone, which is of a similar form, but somewhat 

 larger, may have played a similar part in the hind-foot. 



Comparison of the Bones of the Fore-foot. — In comparing the osseous struc- 

 ture of the fore-foot of the Mylodon with that of existing quadrupeds, a cursory 

 survey would lead to the selection of the Great Ant-eater and the Manis, as 

 ofl'ering the closest resemblance to the M)'lodon in this part of their skeleton ; 

 the fore-foot in both being pentadactyle, with the middle toe conspicuous for its 

 large proportional size, and the rest diminishing to each end of the digital series, 

 whilst the terminal phalanges of the larger toes are provided with an osseous 

 sheath and process for the support and fixation of a long and strong claw, and 

 can only be bent downwards. Of all unguiculate Mammals the Sloths would 



