352 BRITISH FOSSIL REPTILES. 



teeth enabled them to retain, hke barbs, the prey which they had penetrated. In 

 these adaptations we see contrivances which human ingenuity has also adopted in the 

 preparation of various instruments of art."* 



Size of the Megalosaurus. 



A few words may be added touching the size of the Megalosaurus ; for it appears 

 to me that the calculations which assign to it a length of 60 and 70 feet are affected 

 by the fallacy of concluding that the locomotive extremities bore the same proportion 

 to, and share in the support of, the body, as they do in the small modern land 

 Lizards. 



The most probable approximation to a true notion of the actual length of the 

 Megalosaurus is that which may be obtained by taking the length of the vertebrae as 

 tlie basis. The antero-posterior dimension is the most constant which the vertebrae 

 present throughout the spine : in most Crocodilian and Lacertian reptiles the cervical 

 vertebrae are a little shorter than the dorsal ; but these are of equal length, and the 

 caudal vertebras maintain the same length, though decreasing in other dimensions, to 

 very near the extremity of the tail. 



As the dorsal vertebrae of the Megalosaurus agree, in the important character of 

 the mode of articulation of the ribs, with the Crocodiles, it may be regarded as most 

 probable that they also corresponded in their number. This does not exceed 14 in 

 recent Crocodiles, nor 16 in any of the known extinct species ; taking, then, the latter 

 number, and adding to it 7, the usual number of the cervical vertebrae in Crocodiles, 

 we may allow the Megalosaurus 23 vertebrae of the trunk. 



The length of the body of a large dorsal vertebra of the Megalosaurus, in the 

 British Museum, is 4^ inches : from the analogy of the Iguanodon I was led, in my 

 original calculations,! to allow a probable thickness of the intervertebral substance one 

 third of an inch : but if we multiply 23 by 5, not allowing for the probable shortness 

 of the cervical vertebrae, we only then attain a length of 9 feet 7 inches. The sub- 

 sequent discovery of the coadapted dorsal vertebrae, figured in PI. 24 [Dinosauria), shows 

 that their bodies were not separated by soft substance of more than 1 line in 

 thickness. If, moreover, setting aside the analogy of the Megalosaurus to the 

 Crocodiles in the structure of the vertebrae, we take that species of Lacertian which it 

 most resembles in the structure of the teeth, and found our calculation on the number 

 of vertebrae of the trunk in such Lizard, then, the great carnivorous Varanian Monitor 



* Buckland, ' Bridgewater Treatise,' vol. i, p. 237. 



t Report on British Fossil Reptiles, ' Traus. Brit. Association,' 1841. 



