28 THE FOSSIL REPTILES 
arrest the attention of one accustomed to the spongy, solid 
structure in the reptiles. This is especially true of the 
long bones of the hind limbs ; those of the fore limbs have 
a considerably less medullary cavity. The length of the 
femur and tibia render it altogether probable that it 
was plantigrade, walking on the entire sole of the foot 
like the bear. They must also have been very much 
flexed under ordinary circumstances, since the indications 
derivable from two liumeri, or arm bones, are, that the 
fore limbs were not more than one-third the length of the 
posterior pair. This relation, conjoined with the massive 
tail, points to a semi-erect position like that of the Kan- 
garoos, while the lightness and strength of the great femur 
and tibia are altogether appropriate to great powers of 
leaping. The feet must have been elongate, whatever 
the form of the tarsi; the phalanges, or finger bones, were 
slender, nearly as much so as those of an eagle, while the 
great claws in which they terminated were relatively larg- 
er and more compressed than in the great birds of prey. 
There was no provision for the retractibility observed. in 
the great carnivorous Mammalia, but they were always 
equipped with sheaths and crooked points of bone. The 
toes may have been partially webbed, and it is not im- 
probable that the hind legs may have occasionally been 
most efficient propellers of these animals along the coast 
margins of the Cretaceous sea. 
The hind foot could not have been straightened in line 
with the tibia, owing to 2 most anomalous structure which 
has only been once before observed, and then in a species 
clearly referred to its type. The distal head of the fibula, 
or small bone of the leg, appears to have embraced and 
capped the tibia like an epiphysis, and to have given at- 
tachment to ee bones of the tarsus, by a condyle « directed 
Bee es Sat E E 
