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451. The metatarsal bone of the fourth toe, the third in the Mylodon. 



452. The second phalanx, which is the terminal one, of the same toe. 



453. The metatarsal bone of the outermost, corresponding to the fifth toe. 



The two outer metatarsal bones are the only ones of which the size 

 and strength are proportionate to that of the principal bones of the 

 tarsus, the calcaneum and astragalus. That which supports the fourth 

 toe, counting as if the normal number had existed on the inner side of 

 the foot, presents a short trihedral body, expanding into the two ex- 

 tremities. The proximal end is obliquely truncated on the tibial side, 

 with the lower angle produced downwards. A smooth articular surface, 

 slightly concave vertically, and slightly convex transversely, occupies this 

 oblique base, and is divided by a moderate constriction into an anterior 

 smaller ovate surface, adapted to the outer basal process of the middle 

 metacarpal, and into a posterior, vertically elongated larger surface, ap- 

 plied to the tibial anterior facet of the os cuboides. A very slightly 

 concave semi-elliptical articular surface extends obliquely upwards upon 

 the outer side of the proximal end of the bone, and is adapted to a cor- 

 responding convex surface on the adjoining side of the fifth metatarsal. 

 A shallow canal with many vascular perforations surrounds the margin 

 of this surface ; there is a rough tuberosity both above and below the 

 surface. The outer or fibular side of the body of the present metatarsal 

 is rugged and rather flattened : the remaining surfaces are smooth and 

 convex. The distal end of the bone expands in the vertical direction, 

 and supports a narrow, vertically elliptic, convex articular surface, sur- 

 mounted by a large and rough tuberosity, and terminating below in con- 

 cavities, placed somewhat obliquely, for two large sesamoid bones, sepa- 

 rated by a short convex ridge. A narrow ridge traverses vertically the 

 inner side of the distal end of the fourth metatarsal ; and a smooth tu- 

 berosity rises from the middle of the outer side of the same extremity. 



The metatarsal bone of the outer or fifth toe is of extraordinary size 

 and strength ; its length equals that of the adjoining toe ; in the cir- 

 cumference of its base it surpasses the same bone by more than one- 

 half. It presents the form of a rugged and irregular three-sided cone, 



