566 BRITISH FOSSIL REPTILES. 



being thus supported at every point by the matrix, during the slow and continuous partial 

 pressure, the spine has yielded and bent without breaking. In one instance the sustaining 

 neural arcli has suffered partial fracture at the side (ib., fig. 1), toward which the spine 

 has been bent. 



A thickening at the outer side of the neurapophysis, feebly indicated in the larger 

 anterior caudals (PI, 68, fig. 2, np), becomes more prominent near the base of the prezy- 

 gapophysis, as at np, figs. 1 and 2, PI. 69, in the succeeding smaller vertebrae, in 

 which the hypapophyses are more distinctly marked. 



These articular protuberances (ib., figs. 1 — 3, %) form a pair at the hind border of 

 the inferior surface of the centrum ; the articular tracts at the fore border of that surface 

 are barely defined, or may be indicated by an extension backward of the rough marginal 

 syndesmosal tract. 



The caudal vertebra in PI. 69 is figured a little more than half the natural size. The 

 answerable caudals in the great Monitor Lizard {Faranus niloticus) are given, of the 

 natural size, in figs. 4 and 5. 



The haemal arch in the caudal vertebra, with a centrum 5^ inches in vertical extent, 

 has the same length. The haemapophyses (ib., fig. 2, A) are 2f rd inches in length before 

 coalescing to form the spine (ib. ib., A«), which is 2^rd inches in length in the subject of 

 the Plate ; it was probably longer when quite entire. But the length of the arch and 

 spine was plainly less in proportion to the vertical extent of the rest of the vertebra than in 

 Cetiosaurus lonr/us. The hypapophyses are accordingly relatively smaller, and are limited 

 to a narrower transverse extent of the inferior surface of the centrum (ib., fig. 3, hy) than 

 in Celiosaurus, or in the recent Varanus (PI. 69, fig. 4, hj). In Cetiosaurus brevis the 

 hypapophysial facets [h, h) are broader and wider apart than in Cetiosaurus longus. 



In Iguanodon the reverse conditions prevail. These surfaces have become confluent, 

 and present a single bilobed facet to the similarly confluent surfaces on the bases of the 

 rio'ht and left haemapophyses {' Dinosauria,' V\. 13). Both neural and haemal spines 

 are relatively longer in Iguanodon ; and the neural spine springs from a smaller pro- 

 portion of the hind part of the neural arch at a nuich greater distance behind the 

 prezygapophyses than in Omosaurus. The caudal vertebrae differ less from each other 

 in Omosaurus and Cetiosaurus than they do in either of these genera as compared with 

 Iguanodon. 



As in the case of Cetiosaurus longus and other previously described Dinosaurian sub- 

 jects, I have selected the best preserved specimen of an average-sized vertebra for figures 

 of the natural size, the requisite comparisons being much facilitated, and accurate results 

 ensured, by such life-size figures. 



Humerus. — Of the skull, teeth, or scapular arch of Omosaurus I have not as yet 

 received evidence. The humerus and some other bones of the left fore limb (' Dinosauria' 

 PI. 70) have been relieved from the matrix in a more or less complete state. 



