164 NATURAL HISTORY MISCELLANY. 
First. — In the great size, weight and solid condition of the bones of the 
s; gk and in their want of FIRGRIAEX. aaa: 
ond. — In the number, arrangement, 272, mode and unlimited growth 
of iir teeth; in their deep insertion into the jaws; their deeply exca- 
vated base; in the structure of their teeth, when viewed as organs, — 
made up of a cylinder of vascular dentine, dentine and cementum, and 
more particularly in the striking "e of their organization when 
examined under the microscope; t f the Megatherium and Mylodon 
being aput ly the same, with ^s «citta of the looped canals or 
tubules in the cementum, as figured by Prof. Owen in the article Odon- 
tography, i in the ** Encyclopædia Britannica." 
ird. — The bones of the skull resemble each other strongly in the 
Fin development of the cells of the diploé, which in their general ap- 
pearance resemble wood eaten through and through by the largest sized 
worms; and in the shortness of the face. The alveoli of the two jaws 
correspond in number, position and relative depth, with the exception of 
Megalonyx, which has its first molar in the upper and lower jaw sepa- 
rated from the other teeth and taking the usual place of the canine or 
is: teet 
Fourth. ii he bones of the chest and trunk have, in general, a strong 
resemblance in size and form, especially the ribs in size, the scapula in 
form, the expanded ilia, and the clavicles. 'The bones of the hand and 
arm have a marked family likeness — the radius and ulna of Megathere 
and Megalonyx, the humerus of Megalonyx and Mylodon in particular, 
and in all the genera in the broad expansion of the external and internal 
condyles of the humerus for the origin of the supinator and pronator mus- 
cles. The differences between these in outline and form from that o 
Moiktherüsi will be hereafter alluded to. 
Fifth. — The number and size of the bones in the tail of Megatherium 
and Mylodon, and the use to which this appendage is put, appear to be 
precisely the same, making with the posterior extremities a most stable 
tripod for the support of these animals while reaching for their food. 
DERE we hé wood and massive vica of the Megatherium = 
as figured in Leidy's ** Memoir’ 
and | in the ** Penny Cyclopedia " and Snes antes a Britannica,” this bone 
in the prices: appears not to be so o flattened n front, but this. e ania 
resemblance in form to that of Mylodon, but it is not united in either of 
these animals (making as it were one bone) as in Megatherium 
The bone syed pei extinct animals differ somewhat: 
i e general outline of the lower jaw of. Megniberium, espe- 
cially that of ide Cuvieri from South America; less so, however, in that 
part where the teeth are implanted in the N. American Megathere, and 
n its anterior prolongation. 
Second.— The skulls of Megalonyx and Mylodon, looking at them 
either from above or below, differ somewhat, especially in their width; 
