24 • MEGALONYX. 



project backward and outward from the side of the body for about two inches; and 

 they are trilateral, and have a thick tuberous extremity. 



The specimen of a posterior coccygeal vertebra has a transversely elliptical body 

 with an anterior hexahedral and a posterior oval articular surface. Both of the 

 latter are convex, or rather they are centrally very slightly depressed, and at the 

 circumference are bevelled off. The anterior surface is two inches and a third in 

 breadth, by one and three-quarters in depth, and that posterior is two inches in 

 breadth, and one and a half in depth. The inferior surface of the body presents two 

 pairs of short tuberosities for articulation with chevron bones. The spinal canal is 

 open, and is bounded upon each side by a wing-like process, the rudiment of the 

 articular processes. The transverse process is broad and thick, measures two 

 inches in length, and projects outward and backward. 



Hyoid Bone. — The hyoid bone (PI. VII, Figs. 7, 8), of Megalonyx, in comparing 

 it with the figures of this bone of the recent sloths in Blainville's Osteographie, is 

 found to resemble most that of the Unau. 



The specimen in the collection of Dr. Dickeson, is a V-shaped bone, with a pair 

 of anterior tubercles separated by a deep notch, and supporting a circular, shallow 

 concave, articular facet for the cerato-hyal element. The diverging arms of the 

 bone from its anterior angle are about two inches eight lines in length ; and they 

 terminate in a circular convex facet. 



IHibs. — The adult specimen of a rib described by Dr. Harlan,^ consists of about 

 two feet of the vertebral portion, and is peculiarly interesting from its presenting 

 the indications of a fracture, which existed a foot and a half from the head of the 

 bone, and had so well healed that no deformity exists except a convex thickening 

 upon the inner side. This fact is additional evidence in support of the view 

 ingeniously inferred by Professor Owen, that the giant sloths were very liable to 

 accidents not unfrequently involving fracture of the bones, from the habit of up- 

 rooting trees, the boughs of which formed their food. The head of the bone presents 

 a single convex articular facet, and the tubercle another, which is deeply concave. 



Of the several small fragments of ribs in the collection of Dr. Owen, one of them 

 at its broadest part measures two inches. Of the fragments of ribs in Dr. Dicke- 

 son's collection, one is a sternal extremity, and this presents the same form as the 

 corresponding part in Mylodon and the Ai. 



Scapula. — The fragment of a scapula in Dr. Owen's collection, preserves the 

 glenoid articulation, which is ovoid, and is three and a quarter inches long by two 

 and a half wide ; is over an inch in depth from the level of its end margins, but is 

 not more than the fourth of an inch in depth from the level of its side margins. 



Of the portions of both scapulas in the collection of Dr. Dickeson, one consists 

 of the glenoid articulation and coraco-acromial arch of the left bone (PI. VIII, 

 Figs. 1, 2) ; the other of the base and posterior angle of the right one. 



The form of the restored scapula of Megalonyx is very much like that of Mylodon. 



The subscapular fossa presents a strongly folded appearance from the alternation 

 of ridges and sloping surfaces. The ridges converge to the cervix, and the inter- 



» See ante, p. 5; Journ. Acad. Nat. Sci., VI, 271, 2T9, PI. xiv, Fig. 16 ; Med. and Phys. Obs., 321, 326. 



