MEGALONYX. 



37 



The ungual phalanges (PI. X, Figs. 5, 9, 10, 20) consist of a curved, laterally 

 compressed, claw-process, enveloped at the posterior half or two-thirds with a bony 

 sheath rising from an oblong tuberosity on the under border of tlie claw-process. 



The articulation of the last phalanx consists of two vertical concavities separated 

 by an intervening ridge ; and its upper part projects a considerable distance posterior 

 to the lower, or, in other words, overhangs it. 



The claw-process at its upper margin, first obtuse, after a short distance in 

 advance of the sheath, becomes acute. Its sides are nearly vertical ; and they pre- 

 sent beneath the sheath an arborescent vascular channel, which proceeds from an 

 oval foramen piercing each side of the tuberosity from whence springs the sheath. 

 Towards the end of the claw-process its surface becomes more and more perforated ; 

 and it presents numerous fine, reticular, vascular channels, for accommodating the 

 nutritious vessels of the nail. 



The sheath for the reception of the root of the nail is attached around the mar- 

 gin of the articulation, and to the sides of the tuberosity on the under part of the 

 claw-process. Its outer surface is roughened and is perforated for the passage of 

 vessels. 



The tuberosity for the attachment of the sheath, is most prominent near its 

 middle, posteriorly is perforated by the two, large, oval foramina above mentioned, 

 and anteriorly is impressed on each side with a broad surface for attachment of the 

 flexor tendons. From the anterior part of the tuberosity, an abutment springs 

 forth to support the claw process. 



Of the ungual phalanges, that of the median finger (Figs. 5, 9, 10) is the 

 longest and largest, those of the index and annular fingers are next, and are nearly 

 equal in size, and that of the auricular finger is the smallest. What I have taken 

 for the last phalanx of the auricular finger may, however, belong to the hind foot, 

 a fact which I have no certain means of ascertaining. 



Length of first ungual phalanx 

 Greatest depth of first ungual phalanx 

 Length of second ungual phalanx . 

 Depth of second ungual phalanx . 

 Length of median ungual phalanx . 

 Depth of median ungual phalanx . 

 Length of fourth ungual phalanx . 

 Depth of fourth ungual phalanx 

 Length of fifth ungual phalanx 

 Depth of fifth ungual phalanx 





COLLECTION. 





Jefferson' 



s. Owen's 



Dickeson's 



Wailbs 



Inches. 



Inches. 



Inches. 



Inches. 



H 









If 











6 



6 



6* 





H 



2* 



H 



7 



1 



1 



7 



3 



H 



3 



3 



6 



5| 





6 



H 



2^ 





H 



Femur. — (PI. XI, Figs. 1, 2, 3.) The thigh bones o^ Megahmjx, preserved in the 

 collection of Dr. Owen, in form are more like those of the Ai than of Mylodon, but 

 they are relatively very much shorter than in the former animal, and more antero- 

 posteriorly compressed and broader. 



The front of the shaft (Fig. 1) is nearly flat, being slightly concave in the length 

 and slightly convex transversely. Its upper half is marked by two vertical ridges 



