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MEGALONYX. 
ME GAL ONYX. 
( Megalonyx Jeffersonii.) 
This huge terrestrial Sloth, so called for the great size of its claw, is found chiefly in the 
upper tertiary of America. The genus was established by the philosophic President of the 
United States, Thomas Jefferson, in a communication read to the American Philosophical Soci- 
ety, March 10, 1797, entitled “ A Memoir on the Discovery of certain Bones of a Quadruped 
of the clawed hind in the Western Parts of Virginia .” Other remains have been found in 
Tennessee, Kentucky, Mississippi and in Alabama. It resembled the Megatherium in general 
form and habits, but was a third smaller. It is remarkable for the singular expansion of its 
heel-bone, which gives it the appearance of an ilium of some smaller animal. The upper out- 
line of the skull is nearly horizontal. The zygomatic process has a greater vertical diameter 
than in the Mylodon; and the temporal fossa? are separated by a saggital crest, instead of a 
wide, intervening surface. The occipital foramen is sixteen lines in diameter; and the orifice 
of the nose, a little more than three inches across. The end of the face is relatively narrower 
and higher than in the Mylodon. The length of the skull is fourteen inches. The dental 
tormula is M. \ f 18, — the first molars being separated from the rest two inches. As in all 
the Sloth tribe, they are long fangless columns, deeply excavated from the bottom for the pert 
sistent pulp, and composed of dentine and cement. The transverse diameter of the larges 
molar is one inch. The spinal canal, through the atlas and axis is obcordiform, through the 
remaining cervical vertebrae and anterior dorsals it is trilateral, through the posterior dorsals 
it is nearly circular, and through the sacrum it is crescentic. Its greatest diameter is over 
three inches. The clavicles are compressed, cylindroid bones, with a single curvature, and 
two broad surfaces. The length is eight and three-fourths inches. The humerus is twenty 
inches long— being relatively much shorter than in the recent Sloths, but both absolutely 
and relatively longer than that of the Mylodon. The internal condyloid process of the 
humerus is pierced with a large, oval canal — a peculiarity in its anatomy which it does 
not share with any other bradypoid animal. 
