WEALDEN DINOSAURS. 361 



an inferior transverse process in the Dinosaurian sacrum — may be discerned, wedged 

 into the interspace between the second and third sacral vertebras atjj/ 3, and again 

 between the third and fourth vertebrae, at jil 4, fig- 2, PJ. 36. 



A third portion of the sacrum of the Hylaeosaurus, which escaped the cognizance 

 of the authors of the paper in the ' Philosophical Transactions ' for 1 849, is the specimen 

 No. 28,936, British Museum, PI. 37, figs. 2, 3, 4. This consists of the third sacral 

 vertebra, with part of the second and fourth anchylosed therewith, a great proportion of 

 the neural arch, and a small part of the left ilium being included in this very instructive 

 specimen. It is from the submerged Wealden of the Isle of Wight, and has been 

 subject, like many of the fossils from that locality, to a certain degree of attrition by 

 sea-waves on the beach. 



The pleurapophysis (fig. 3, pi 3), continued from the obliterated interspace between 

 the third and second vertebrae, quickly assumes the form of a broad and high plate, 

 compressed from before backwards, and again becoming thickened when it abuts 

 against the ilium (62). 



The diapophysis (fig. 4, d 3), arising from the side of the neural arch, seems to 

 form the upper part of the same broad, vertical, transverse wall of bone ; but the 

 suture between the pleurapophysial and diapophysial elements of this wall is clearly 

 traceable, extending from the base of the neurapophysis upwards and outwards. The 

 diapophysis at its upper part expands, and seems to bifurcate or abut against the side 

 of the base of the neural spine. This spine forms, at the part of the sacrum here 

 described, a continuous ridge of bone. 



The fractured outer border of the ilium has been rounded and water-worn to its 

 present form, which must not be taken as indicating its natural one. A large vacuity 

 was bounded by the ilium and the two contiguous diapophysial plates (fig. 3), as in 

 the sacrum of the Iguanodon : the large nerve-outlet, formed by the receding borders 

 of contiguous neural arches, and the middle part of the centrum, opens into the large 

 space above defined. 



Caudal Vertebra. PI. 41. 



A proportion of the tail, to the extent of nearly six feet, and including about 

 twenty-six vertebrae, discovered in a quarry in Tilgate Forest in the year 1837, is 

 preserved in the British Museum (PI. 41). The diapophyses {d, d) present almost 

 Crocodilian proportions, in regard to their length, at the interior part of this series, 

 and may be discerned, though diminished to mere rudiments, in the small terminal 

 vertebrae of the series. In the most perfect of the anterior vertebrae they are com- 

 pressed vertically, but with convex, not flattened sides, and rounded edges, presenting 



