Mr. Owen on the Glyptodon clavipes. 95 



depression : from the very slight extent of motion allowed by these flattened arti- 

 culations of the toes, one cannot be surprised that the synovial bag should be in 

 part obhterated, as these rough places in the centre of the articulating surfaces 

 would seem to indicate. The form of the anterior articulating surface of the second 

 phalanx is shown in PI. XIL fig. 3. 



The distal or unguial phalanx of the second toe * presents a very remarkable 

 form ; it is suddenly expanded, in breadth and depth, immediately beyond the 

 articular facet for the preceding phalanx, and this facet appears thus to occupy 

 only the middle of the posterior surface, and to be surrounded by a broad rough 

 margin. This surface is not placed at right angles to the long axis of the phalanx, 

 but slopes from above downwards and forwards at a very acute angle with the 

 upper surface, so that the apex of the phalanx points almost directly downwards ; 

 the inferior boundary of the posterior surface forms a rough ridge, separated by a 

 smooth narrow concavity from the anterior border of the phalanx : the superior 

 sloping surface is shghtly convex, and deeply pitted and sculptured with vascular 

 grooves and impressions. 



The unguial phalanx of the third toef is broader but shorter than the preceding, 

 and is of a more symmetrical figure : the lower margin of its posterior surface 

 forms a broader ridge, and the articular surface is a little more convex, but the 

 resemblance is otherwise very close. The unguial phalanx of the fourth toe has 

 the same general form as the preceding, but is smaller ; like the last phalanx of 

 the second toe, it is unsymmetrical, but from a diflTerent modification : in the 

 second toe the inner margin is rounded oflf towards the outer ; in the fourth toe the 

 outer margin is rounded off towards the inner. The middle phalanx of the third | 

 and fourth toes is more square-shaped and broader than that of the second ; it 

 has the same general compressed form, with nearly flat articular surfaces, but, 

 being narrower above, it resembles an inverted wedge ; it is also notched, but less 

 deeply, below, and has an articular facet for a sesamoid bone on each side of the 

 notch. 



When the bones of the hinder extremity above-described are arranged in their 

 natural relative positions, they present to our observation the framework of a foot 

 of such a construction and form as I may venture to say is without a parallel in 

 the animal kingdom : the nearest approach to its broad, thick, short, and massive 

 proportions is made by the skeleton of the fossorial extremity of the Mole ; but 

 it is the fore-foot only of this animal that can be compared, in the compressed 

 bulky figure of the metacarpals and proximal and middle phalanges, with the 

 singular hinder extremity of the Glyptodon above-described. The hind-foot of the 

 Mole resembles, in the lengthened metatarsal and phalangeal bones, that of the 



* PI. XIL fig. 1, 3 ; fig. 5. t Ibid, fig, 6. % Ibid, fig. 4. 



