42 MEGALONYX. 



the articulation for the apophysis of the astragalus, and is formed by a bi'oad 

 conical prominence bounded below by a deep, crescentic concavity. The anterior 

 surface (Fig. 8) presents a pair of vertically oblong, articular facets, separated by 

 a shallow gutter, of which the outer one joins the external cuneiform bone, the 

 inner the contiguous cuneiform bone. 



Inches. 



Greatest vertical diameter of scaphoid bone ... . ' . . 3^ 



Greatest transverse diameter . . . . 2| 



Greatest antero-posterior diameter, from tlie summit of tlie articular cone posteriorly IJ 



Os Canei/orme Externxhm. — (PI. XIII, Figs. 1, 2, 3.) The external cuneiform 

 bone is the smallest of those of the tarsus which have been described. It is 

 irregularly, flattened pyriform, with its dorsal extremity (Fig. 1) thickest and 

 broadest. Posteriorly (Fig. 3), it presents a vertical, concave facet, extending the 

 depth and breadth of the bone, to articulate with the scaphoides, and this facet is 

 joined at an obtuse angle supero-externally by a small one for the cuboides. Ante- 

 riorly (Fig. 2), the external cuneiform bone is occupied by a vertical, convex facet, 

 constricted at the middle and broadest above, for articulation with the third metar 

 tarsal bone. 



Inches. 

 Greatest depth of external cuneiform bone ........ 3 . 



Greatest breadth ............ 2 



Greatest antero-posterior diameter, superiorly l^ 



Metatarsus. — Of metatarsal bones, there are in the collection of Dr. Owen, a 

 second of one side, and the fourth and fifth of both sides. Of the three bones 

 indicated, the second is the shortest and the fifth the longest. 



The second metatarsal bone (PI. XIII, Figs. 9, 10, 11) has a trilateral diaphysis 

 with the dorsal surface broadest and most deeply concave antero-posteriorly. 



The proximal extremity (Fig. 11) is triangular, the angles being tuberous and 

 prominent. The tarsal articulation is concave, but which bone it especially joins I 

 have not the materials to ascertain. The inner angle internally is furnished with 

 an oblique, oval, slightly concave facet (Fig. 9), for articulation with the first meta- 

 tarsal, and the outer angle externally presents a circular, nearly plane surface (Fig. 

 10), for junction with the third metatarsal. 



The distal extremity (Fig. 9) of the bone is constructed after the pattern of that 

 of the metacarpals, consisting of a long, vertical, ellipsoidal, articulating process, 

 with a short vertical offset upon each side. 



Inches. 

 Length of second metatarsal bone ......... 3|- 



Breadth of the diaphysis . . - If 



Depth of the proximal end, from the inferior angle to the middle of the base 



of the triangle . . . . . . . . . . . • 2J 



Depth of the distal articulation 2^ .' 



The fourth metatarsal bone (PI. XIII, Figs. 12, 13, 14, 14*) has a cylindroid 



