﻿KIMME RIDGE CLAY. 



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§ 17. Dermal Spine. — One osseous spine (PI, XXI, figs. 1 and 2 ; PI. XXII, 

 figs. 2 and 3) has been successfully wrought out of the matrix ; but though a close 

 search was made for other evidences of a dermo-skeleton none have been found. 



The spine in question is 1 foot 6| inches in length, and not more of the tip seems 

 to be wanting than might extend this dimension to 1 foot 7 inches, or, at most, 1 foot 

 8 inches ; the long diameter of its base (PI. XXII, fig. 2) is 5 inches ; the shaft gradually 

 tapers to a point. The spine is rounded and slightly compressed ; the narrower diameter 

 is shown in Plate XXI, fig. 1, the greater breadth in ib., fig. 2. The surface, smoothest 

 toward the base, becomes slightly broken by fine longitudinal, quasi fibrous, markings ; 

 and this sculpturing becomes coarser as the spine contracts. At every part may be seen 

 small orifices, apparently vascular ; few in number along the basal two thirds, but more 

 frequent near the point. These indicate a periosteum in relation to the supply of a 

 horny sheath, of which we have here the petrified bony core. The texture of the osseous 

 substance is dense (PI. XXII, fig. 3). 



The base is obliquely truncate, with a boldly sculptured border, broadly and deeply 

 notched as if for strong ligamentous attachments, the whole basal surface being coarsely 

 roughened ; it is also channelled, seemingly, by two vessels entering the substance of the 

 spine, one, perhaps, an artery, the other a vein (PI. XXII, 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, 1 but they are succeeded by symmetrical dermo-neural spines having a 

 medial position along the rest of the trunk and tail. 2 



The osseous spines, probably dermo-neural, of Hglaosaurus, 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 unsymmetrical in 

 shape, but in a greater degree ; and they are much more compressed. 3 



In the Hyla30saurian 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 pair of depressions or canals above noted, 

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



1 Pal. Monogr., ' Scelidosaurus,' vol. for 1860, p. 25. 



2 Ib., p. 22, pi. ix, figs. 1, 3, 5. 



3 Pal. Monogr., ' Wealden Reptilia,' vol. for 185 6, pp. 23-26, pi. iv, pi. ix. 



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