370 BRITISH FOSSIL REPTILES. 



Fossil Reptiles,' in 1840, with the means of submitting the structure of a dermal scute 

 of the Hylaeosaur to microscopical examination. This structure is represented in PI. 40, 

 fig. 1 , and was described in my ' Report ' as follows : 



" The medullary canals, which are stained brown, as if with the hematosine of the 

 old reptile, differ from those of ordinary bone in the paucity or absence of concentric 

 layers. They are situated in the interspaces of straight, opaque, decussated filaments, 

 which frequently seem to be cut short off close to the medullary canals. Very fine 

 lines may be observed to radiate from some of the medullary canals : irregularly shaped, 

 oblono-, and angular radiated cells are scattered through most parts of the osseous 

 tissue, but they present less uniformity of size than do the Purkinjian cells in ordinary 

 bone. The most striking characteristics of the dermal bone are the long, straight, 

 spicular fibres which traverse it, and decussate each other in all directions, repre- 

 senting, as it seems, the ossified ligamentous fibres of the original corium."* 



JJermal Spines ? Pis. 35 and 40. 



On the left side of the thorax, partly overlying the left scapula and vertebral ribs 

 in the large slab of stone containing the anterior part of the skeleton, now in the 

 British Museum, there are some large elongated, fiattened, pointed plates of bone, three 

 of which seem to follow each other in natural succession (PI. 35, d, d, d)- The length 

 of the first of these plates is 17 inches, the breadth of the base 5 inches, equal to the 

 antero-posterior diameter of two vertebrae : they decrease somewhat rapidly in length, 

 the second being 14 inches long, and the third 11 inches long; but they slightly 

 increase in breadth. 



These remarkable bones were regarded by Dr. Mantellf as having formed part of a 

 serrated fringe extended along the back of the animal, analogous to that of the Cyclura 

 Lizard. The chief objection, though not decisive, against this view is, a want of 

 symmetry in the form of the most perfect of them. They are nearly flat, but along 

 the middle present a slight degree of concavity towards the observer, which, however, 

 I once thought " might be paralleled by a similar concavity. on the oposite side buried 

 in the stone -,"1 but a separate specimen since obtained proves that side to have 

 been convex (PI. 40, fig. 3) ; and the anterior margin in the bones {d, d, PI. 35) inchnes 

 from the middle line towards the concave side. 



"With regard to their relative position to the rest of the skeleton, it must be 

 remembered that the ventral surface of this is exposed (PI. 35) ; so that the under 



* lb., p. 115. 



f ' Geology of the South-east of England,' p. 323 j ' Wonders of Geology,' vol. i, p402. . 

 J 'Reports of British Association,' 1841, p. 116. 



