ARTICLE IX. 
REMARKS ON THE STRUCTURE OF THE FEET OF MEGALONYX. 
BY JOSEPH LEIDY, M. D. 
[Read Dec. 19, 1856.] 
‘ 
ty the Smithsonian Contributions to Knowledge entitled “A Memoir on the Extinct Sloth 
Tribe of North America,’ I attributed five toes to the hinder-feet, as well as to the fore-feet of 
the Megalonyx :—a greater number than is known to belong to any other genus of the Gravi- 
grada. At the time of writing the memoir, I had only had the opportunity of seeing the 
second, fourth, and fifth metatarsal bones of the Megalonyx. Prof. M. Tuomey recently pre- 
sented to the Academy of Natural Sciences, a collection of bones of the Megalonyx, dis- 
covered in a cave in the northern part of Alabama. In this collection there is a com- 
plete series of metatarsals, as represented in fig. 1, plate 6, except the first one, or that 
belonging to the inner side of the foot. 
The middle metatarsal bone is the shortest of the outer four, but it is much more robust 
in its proportions transversely and vertically, in accordance with the great size and strength 
of the middle toe. Its shaft is quadrate, but is so short as to appear to be formed simply 
by the conjunction of the carpal and phalangial extremities. The latter extremity is com- 
posed of three vertically convex lobes of which the median one is three and a quarter 
inches in depth. The carpal articular surface extends the entire depth of the corresponding 
extremity, and is quadrate and moderately concave. The articulation for the base of the 
second metatarsal bone, is a convex, oval surface, supported at the upper angle upon a pro- 
minent tuberosity. In a corresponding position, externally there is a rounded concave sur- 
face for articulation with the base of the third metatarsal bone. 
The last metatarsal bone of the left foot presents a remarkable variation from that of the 
one figured; the interval between the shaft and long basal process being filled up, so that 
the bone is, in this specimen, a thick triangular plate with the carpal and fourth metatar- 
sal articular surfaces placed on each side of its inner angle. 
The measurement in length of the four metatarsals represented, is 3 inches for the second, 
22 for the third, 4% for the fourth, and 5 for the fifth. 
