MEGALONYX. 35 



The auricular metacarpal bone (PI. X, Figs. 18, 19), in the collection of Jefler- 

 son, has a cylindrical shaft, which expands most posteriorly. 



The proximal end is irregularly pyramidal with the base outward, and with the 

 apex tuberous. The outer side (Fig. 19) presents a slightly concave reniform facet 

 for junction with the annular metacarpal, and the inner side is marked by a con- 

 spicuous discoidal surface of attachment for the internal carpo-metacarpal ligament. 

 The carpal aspect presents a reniform, bent, articular surface bounded above by a 

 thick rough ridge. The upper portion of this surface is for junction with the unci- 

 forme, and that below and internally is for the cuneiforrae. 



The distal end is formed by a vertically oblong process with an anterior, con- 

 vex, articular facet, bounded by a thick, obtuse ridge (Fig. 19). 



Inches. 

 Length obliquely ............ 4J 



Circumference of sliaft at middle .......... 3 



Depth of proximal end . . . . . . . . . . • IJ 



. Depth of distal end IJ 



The auricular metacarpal bone of the Mefjalonyx, Cuvier at first mistook for the 

 annular metacarpal,^ and was subsequently misled to view it as belonging to the 

 index finger.^ These mistakes probably arose from the examination only of a cast of 

 the bone, in which the discoidal surface for the attachment of the internal carpo- 

 metacarpal ligament could not well be distinguished from an articular facet. 



The auricular metacarpal in the collection of Col. Wailes is broken, but when 

 perfect, it appears to have been exactly like that above described. 



Phalanges. — Of first phalanges, the collection of Dr. Owen contains an index, 

 both median, and one annular; that of Jeflferson, a median; that of Col. Wailes, 

 the index, median, and annular of the left hand ; and that of Dr. Dickeson, an 

 index and a median. 



The first phalanges (PI. X, Figs. 3, 7) are deeper than they are long, and are 

 curved pyramidal, with a rounded apex above and a transversely concave base 

 below. 



The proximal or metacarpal articulation is a deep, vertical concavity, extending 

 from top to bottom of the bone, with an offset on each side inferiorly in the median 

 phalanx, but on one side only in the annular and index phalanges. 



The distal articulation consists of a trochlea, composed of two vertical, conjoined 

 convexities projecting from the anterior aspect of the bone, bounded above and 

 below by a concave surface, to increase the extent of flexion and extension of the 

 second phalanges. 



Of the three fii'st phalanges indicated, the median is the largest, whilst the other 

 two are nearly equal in size. 



' Annales dii Mus. d'Hist. Nat., V, 369. 

 » Ossemens Fossiles, VIII, 302. (2d Ed.) 



