AND AVES OF NOKTH AME1UCA. 



115 



must have rendered them far less efficient as weapons than the hind feet, in an attack on 

 such a creature as Eadrosaurus ; hence perhaps the latter were preferred in inflicting fetal 

 wounds. The ornithic type of sacrum elucidated by Prof. Owen, suggests a resemblance 

 in the use of the limb." 



There were but few animals then living which could afford long pursuit on land, so 

 far as known, excepting among the Dinosauria of that day. The Laelaps had to contend 

 with hard-shelled turtles or armored crocodiles, or the swift sea-saurians. These it must 

 capture by sudden movements, as it is not likely that its grasping Iocs furnished much 

 natatory power. 



The lightness and hollowncss of the bones of the Laelaps arrest the attention. This 

 is especially true of the long hones of the hind limbs; those of the fore limbs have a. less 

 considerable medullary cavity. In this respect they are quite similar to those of Coelo- 

 saurus Leidy, of which its describer remarks that " the medullary cavity of the tibia, is 

 Large, and the walls thin, and dense," "being intermediate in this respect between the 

 characters of the Mammals and Birds." 



The mutual flexure, as well as 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 toe bones were slender, nearly as 

 much so relatively as those of an eagle, while; the great claws in which they terminated 

 were relatively larger and more compressed than in the birds of prey. There was no 

 provision for the retractibility observed in the great carnivorous mammalia, hut the size 

 of the inferior basal tuberosity indicates the insertion of a great tendon of a powerful 

 flexor muscle. The slight grooves at the base, and deeper one on each side of the pha- 

 lauge, indicate the usual horny sheath, which, prolonging the point of the claw, would 

 give it a total length of ten inches. 



The tail was moderately long, rounded and strong, and not so much a support as capa- 

 ble of striking a, blow and of throwing an enemy within reach of the kick or grab of the 

 terrible hind leg. 



The fore limbs must indeed have- been of very little use, and it is very difficult to 

 imagine an animal both running and seizing the prey it overtakes, with the hind limb. If 

 it were not a carrion feeder it must have Leaped. We are informed by Hoohstetter* that 

 the Apteryx leaps with. the utmost ease over objects two and three feet in height, that is, 

 higher than its head. Huxley suggests that the Compsognathus "hopped" along on its 

 hind limbs. The bulk of Laelaps is no objection to its leaping, for the giant extinct kanga- 

 roos, Macropus atlas and titan, found in the postpHocene caves of Australia, did not fall far 

 short of these reptiles, in this respect. We may add that Laelaps had smaller allies, as 



* New Zealand Amer. Trans., 181. 



