M E G A L O N Y X . 33 



On each side of the distal extremity a tuberosity exists for the attachment of the 

 lateral ligaments. 



. Inches. 



Length 3? 



Circumference of shaft ........... 3J 



Depth of proximal extremity . . . . . . . . . • IJ 



Depth of distal extremity 2 



Cuvier was misled by comparison of the index metacarpal of the Megalonyx with 

 the metacarpals of neighboring genera of animals, to consider it as that of the 

 annular finger/ although its exact adaptation to the radial side of the median 

 metacarpal had previously led him to indicate its true position." 



The specimen of an index metacarpal, in the collection of Jefferson, is shorter and 

 relatively more robust than that described ; and the articular fticets of its proximal 

 extremity differ a little in form. The surface for the trapezoides is more depressed, 

 and its outer angle more prolonged. The facet for the median metacarpal is more 

 concave; and that for the metacarpal of the thumb is narrower, more regularly 

 demi-pyriform, and is slightly depressed. 



Inches. 

 Length . . . . . . . . . . . '. . -3^ 



Circumference of shaft . . . . . . . . . . .33 



Depth of proximal extremity . . . . . . . . . • IJ 



Depth of distal extremity ........... 2 



The index metacarpal, in Dr. Dickeson's collection, is almost equal in size to that 

 first described, but its shaft is more cylindroid. The carpal articular facet is inter- 

 mediate in the depth of its concavity to that of the above two specimens, and its 

 outer angle is more prolonged than in either. The contiguous metacarpal facets 

 have almost the same outline, but are nearly planes. 



Inches. 



Length . 3^ 



Circumference of shaft ........... 3^ ' 



Depth of proximal extremity 1} 



Depth of distal extremity IJ 



The diaphysis of the median metacarpals (PI. X, Fig. 2, 6, 13, 14), of Dr. Owen's 

 collection, is quadrilateral. The dorsal side (Fig. G) is broadest, and the palmar 

 and inner sides, which are nearly equal, are narrowest. Antero-posteriorly the sur- 

 faces are more or less concave, that on the palmar aspect being most so. The inner 

 side, just in advance of its middle is crossed by a tuberous ridge, which also extends 

 to the distal articulation. 



The proximal extremity (Fig. 13) is pyramidal, with the apex, which is down- 

 ward, obliquely truncated, the base deeply excavated, and the outer side deeply 

 grooved. The carpal articulation is trilobed, with the odd lobe downward. Viertically, 



« Ossemens Fossiles, VIII, 320. (4th Ed.) 

 '' Annalcs du Mus. d'llist. Nat., V, 307. 



