AND AYES OF NORTH AMERICA. 



Ill 



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the body, as the animal was famished with a tail of greater or loss weight. This member 

 bears however little proportion to the great size of those seen in Iguanodon, Hadrosaurus, 

 etc., but exhibits a commencement of the reduction which is so striking among the birds. 



The proportions of the metatarsus are only to be ascertained by an examination of those 

 of allied species, as L. macropus and Megalosaurus bucklandii. As all the other bones 

 are more slender than those of the latter, so were no doubt these bones longer in propor- 

 tion to their breadth. 1 have estimated it above, as equal to a little over half the tibia. 



The digits in the genus Laelaps have not in all probability, been more than three. 

 The less bird-like forms of Hylaeosaurus and iguanodon, have had according to Owen, but 

 three metatarsals, and it is not according to the rule of successional relation, that there 

 should be any repetition of a reptilian character, in a point of prime importance in mea- 

 suring the steps of succession between reptiles and birds. Laelaps and probably Megalo- 

 saurus, also, had but three digits directed anteriorly, and a fourth rndimental. 



It is true that Deslongchamps ascribes five digits to Poecilopleurum after a careful 

 study o I' abundant material. He was however much more impressed with the crocodilian 

 affinities of that reptile than with any other, and did not recognize tin 1 avine in the astra- 

 galus. It seems to me quite possible that one of his toes can be dispensed with, for exam- 

 ple the second, of which but one phalange is said to remain. If we ascribe the fractured 

 extremity of tin; bone; regarded (Tab. VIII.,]). (>,) as the first phalange of the fourth digit, 

 to the metatarsal of the same, the phalange referred to the second may find another place. 

 The fifth digit also rests on the evidence of one phalange only. Though the reasoning of 

 Deslongchamps in referring these pieces is good, it seems to me that renewed study might 

 result in ascribing to his genus, three toes anteriorly and one- appendicular, his first. 



The predominance of reptilian characters in the Dinosauria as indicated by the struc- 

 ture of the vertebrae, and other points, renders it probable that tin- vertebral column did 

 not present that remarkable flexure where the cervical and dorsal series are joined, which 

 is seen in the birds, but rather that they were more or less continuous, and formed a, con- 

 tinuum from the sacrum to the nape. The cervicals may have been somewhat elongated 

 as in some birds, yet this is not probable in view of the necessary balance to be preserved, 

 which would not adroit of much projection of the cranium anteriorly. The cervicals of 

 Hadrosaurus are not so long as in the modern Varani; in Iguanodon they are similar, while 

 their rather oblique articular faces indicate the elevation of that region, and of the position 

 of the cranium. In the case of these animals, there is not the same necessity for a long 

 neck as in flu; birds, lor even in Laelaps and. other genera, which probably never used the 

 fore limbs in progression, they furnished a, support to the body when the head was em- 

 ployed in taking food, etc., in the ground. 



The caudal region affects tin 1 general proportions of a vertebrated animal materially. 



