578 BRITISH FOSSIL REPTILES. 



spine, one, perhaps, an-artery, the other a vein (PL 75, fig. 2). The spine is traversed 

 by a central medullary or chondrosal canal, in diameter one third that of the smaller 

 diameter of the spine (ib., fig. 3). The rough imperforate part of the base, like its 

 coarse periphery, suggests adaptation to syndesmotic junction with some other bone. 

 But with what part of the frame? 



There is a want of symmetry at the obliquely truncate base, which suggests this 

 spine to have been one of a pair. 



In Scelidosaurus the dermo-neural spines at the neck and fore-part of the back are 

 similarly ' somewhat unsymmetrical in form,' showing a parial arrangement along that 

 part of the trunk, but they are succeeded by symmetrical dermo-neural spines having a 

 medial position along the rest of the trunk and tail. 



The osseous spines, probably dermo-neural, of Hylceosaurus, show a length in propor- 

 tion to the adjacent vertebral centrums somewhat exceeding the present spine of 

 Omosaurus ; they are, likewise, obliquely truncate at the base, and misymmetrical in 

 shape, but in a greater degree ; and they are much more compressed (' Dinosauria,' 

 PI. 37, d). 



In the Hylseosaurian specimen in the British Museum, which turned the scale in favour 

 of the dermo-neural hypothesis, an irregular angular depression is described and figured at 

 the base ; and this repeats, though single, the i)air of depressions or canals above noted, 

 and reputed vascular, in the base of the spine of Omosaurus. The low, obtuse, thick ridge 

 girting the base of the spine in Hylceosaurus is, however, simple, unnotched ; the 

 provision for attachment of the spine, in Omosaurus, betokens a greater power of 

 resistance against displacement. The superior strength of the spine, due to its full 

 elliptical sha[)e in transverse section, suggests its application as a weapon to be wielded 

 for attack rather than as one of a merely defensive palisade of spines. 



Considering the number of vertebrae — dorsal, sacral, caudal — which have been recovered 

 in more or less completeness from the intractable mass of some tons weight, including the 

 rest of the above described recovered parts of the skeleton of the Omosaur, it might 

 reasonably be expected that, had the trunk and tail been defended by dermal spines, as in 

 Scelidosaurus and Hylaosaurus, especially by spines similar in number and arrangement 

 to the dermal ridged scutes in the more Crocodilian Dinosaur of the Lias, evidences 

 of such appendages to the trunk-skeleton should have been found in the grave of the great 

 Kimmeridgian dragon. 



But we are, now, not limited to the head, the trunk, or the tail in quest of positions 

 of armour afforded by dermal bones to extinct members of the Reptilian class. 



In the great Mantellian Iguanodon, or at least in the male of that species, a pair of 

 spines supported by unsymmetrical conical bony cores were wielded for offensive action by 

 the fore-limbs (p. 508, Pis. 46, 47). The form and proportions of the Iguanodontal 

 carpal spine, especially in its degree of compression, are more like those of the spine in 

 Omosaurus than are any of the dorsal spines in Hylceosaurus. True, the conical spine- 



