122 DINOCEEATA. 



The Second Metacarpal. (Plate XXXV, figures 7-12.) 



The metacarpal supporting the second digit in the Dinocerata is 

 nearly twice as long as the first, but not greatly wider, nor thicker. The 

 shaft is strongly roughened and tuberculated near each end, as shown in 

 Plate XXXV, figures 7-10, while the middle portion is much smoother. 



The proximal end of the bone presents three distinct, but confluent, 

 articular faces, of which the fii'st, beginning on the radial side, is the 

 largest. It met the trapezoid, and furnished the principal support of that 

 bone. This face, shown in figure 11, is oblique to the axis of the bone, 

 throwing it, in its natural position, well toward the radial side of the 

 manus. It is a little broader, and more oblique, above than below, and is 

 slightly concave in both directions. 



A second adjoining face, shorter and smaller, shown also in figure 11, 

 is nearly perpendicular to the axis of the bone, slightly narrowed behind, 

 and convex in both directions. In life, this face articulated with the 

 oblique distal face of the magnum. 



A third face, on the idnar .side of the bone at the proximal end, shown 

 best in figure 10, articulated with a similar face on the adjoining third 

 metacarpal. 



The distal end of the bone (figure 12) bears a broadly oval, only 

 slightly convex, articular face for the phalanx. This is encroached upon 

 below, by the broad, shallow grooves for sesamoid bones. 



I'he principal dimensions of the second metacarpal repi'esented in 

 Plate XXXV are as follows : 



Measurements of Second Metacarpal. (Dinoceras mirabile. No. 1208.) 



m. 



Total length of second metacarpal, J - .102 



Diameters of pro-vimal end, 039-.065 



Diameters of distal end, _ .046-058 



Diameters of sbaft, _ _ _ - . .030-040 



Antero-posterior diameter of face for trapezoid, .. .050 



Transverse diameters of face for trapezoid, - -- .020-023 



Antero-posterior diameter of face for magnum, - .046 



Transverse diameters of face for magnum, _ _ .012-.018 



Antero-posterior diameter of face for third metacarpal, . .040 



Diameters of face for phalanx, .025-.041 



