320 PEOI^SSOE OWIS^ ON THE MEGATHEEIOL 
The great terminal phalanx of the present toe (Plates XL. & XLI. Hi, 3) is modified, 
like its homotype on the fore foot, for the firm fixation and development of a powerful 
claw, the hollow base of which covered the bony core, and was encompassed by a bony 
sheath of 6 inches in length. _ 
The base of the phalanx, whence both core and sheath extend forward, is a surface of 
a long, narrow, vertically elliptical form, with the upper third produced backward so as 
to overhang or cover the confluent supporting phalanges ; and the lower third slopmg 
forward at nearly the same angle with the vertical middle third, but tenmnated by a 
backwardly projecting ridge. There are two articular surfaces on the middle division, 
two on the upper division, and one on the lower division of the base. The innermost 
of the middle articulations is slightly convex, the outermost as slightly concave; they 
both look directly backward. The lower articular surface is flat and subcircular ; it is 
on the hinder and outer angle of the lower third of the base, and looks downward and 
a little backward ; the two small surfaces on the upper third of the base are subcircular 
and flat, and look downward : these different articular surfaces are counterparts of those 
on the distal and upper parts of the connate phalanges.^ On each side of the lower 
third of the base of the claw-phalanx is a large canal, leading forward to the interspace 
between the bony core and sheath of the claw, and giving passage to the vessels and 
nerves of the formative matrix of that instrument. The tibial side of the sheath 
(Plate XL. fig. 1, 3 ) is gently convex ; the fibular side (Plate XLI. fig. 3, 3 ) is flatter : a 
similar modification affects the claw-core, the narrow basal part of which is divided by 
sharp borders from the sides. The point of the core projects* about^ 3 inches in advance 
of the lower border of the sheath: its form, broken in the specimen, is restored in 
dotted outline in the figures. 
The distal articular surface of the fourth metatarsal shows that it supported a phalanx 
so articulated with it as to have no movements of flexion or extension, and only a shght 
degree of bending from side to side. The illustrations of the Madrid skeleton, especiaUy 
plate 6, fig. 6, show that this phalanx (Plate XLI. fig. 1, iv, :) was very short, and that 
it supported a second phalanx (ib. w, 2 ) of a subhemispheric form, terminated obtusely. 
The distal articular surface of the fifth metatarsal indicates that it supported a pha- 
lanx smaller than the proximal one of the fourth toe ; and the figure, abo\e cited, of the 
Madrid skeleton shows such a phalanx (ib. v, 1 ), and also a second small stunted hemi- 
spheric phalanx (ib. v, 2 ) * ; and this, from the analogy of the Mylodon, is most probably 
the true structure. 
If we contemplate the bones of this singularly constructed foot in their natuml 
* In the original memoir, by Bnv and GASEiaA, on the Skeleton of the Megatherium at Madrrt, the 
metatarsus and toes of the hind foot are said to agree with those of the fore foot, except that there is only 
one toe with a claw, instead of three (“ Tamhien se advierte qiie en este hay solo nn Dedo con nna, quando 
en la Mano se registran tres ; en lo demas convienen en nn todo,” p. 16). In the description of the outer- 
most (fourth developed) toe of the fore foot it is stated that it has two phalanges, and that there is 
nothing to he remarked except that they are rounded (“Los^dos Falanges del quarto qne se reconocen en 
J. y L. no tienen cosa qne advertir mas qne son casi redondas, p. 13). 
