MEGALONYX. 4;] 



shaft, deeply concave antero-posteriorly above and below, but most so in the latter 

 position. 



The proximal extremity {li''% the figure is reversed) is quadrilateral with the 

 lateral sides longest and the lower side shortest. It is bounded above by a thick 

 transverse ridge, and inferiorly forms a prominent pyramidal tuberosity. The 

 tarsal articulation (Fig. 14'==) consists of a single, vertically oblong quadrilateral 

 plane, for junction with the cuboides. The outer side (Fig. 14) presents a large, 

 quadrilateral plane, continuous with the cuboid articulation and prolonged at its 

 postero-inferior angle, for junction with the fifth metatarsal. The inner side (Fig. 

 13), at its upper part, supports a transversely elliptical, convex facet for articula- 

 tion with the third metatarsal. 



The distal extremity is constructed like that of the bone last described, except 

 that no articular offset exists upon the outer side. 



Inches. 



Length of fourth metatarsal bone 4^ 



Circumference of the diaphysis 4^ 



Height of the proximal extremit}' 2^ 



Height of distal extremity 2^ 



The fifth metatarsal bone (PI. XIII, Figs. 15, 16) is quite peculiar in its form, 

 arising chiefly from a huge process projecting obliquely outward and backward 

 from the carpal extremity of the normal diaphysis. Viewed as a whole, it is trian- 

 gular with the angles tuberous, the margins concave, and the dorsal and plantar 

 surfaces concave and shelving forward and outward. 



The normal diaphysis is compressed cylindroid, with an acute outer and a convex 

 inner border. 



The lateral process is stronger and broader than the diaphysis of the bone, and 

 is about the same length. Its extremity forms a convex tuberosity, and inferiorly 

 also presents a pair of low, rough tuberosities. 



The tarsal extremity of the bone presents two, irregularly semicircular, vertical, 

 slightly concave facets, conjoining at an acute angle. The tarsal facet (Fig. 16) 

 articulates with the cuboides ; the other one joins the fourth metatarsal bone. 



The distal extremity of the bone forms a large convex tuberosity, supporting a 

 single, elliptical, convex, articular facet for the first phalanx. 



Inches. 

 Length of the fifth metatarsal bone, from the angle formed ))y tlic articular facets 



of the tarsal extremity to the distal end 3^ 



Length from angle formed by the articular facets of the tarsal extremity to the 



lateral process . . . . • • • • • • • . 3J 



Depth of tarsal extremity 2 



Depth of distal extremity 1' 



Width of shaft anterior to the lateral process 1^ 



Width of lateral process 2 



Phalanges.— Oi phalanges of the hind foot of Megalonyx, the collection of Dr. 

 Owen contains the homologue of the first and second of the middle toe ; the last 



