114 REPORT — 1841. 



body, exposing its solid minutely cellular central structure : its neural arch 

 is too mutilated for profitable description : its base rests nearly equally on 

 the second and third sacral bodies. The third neural arch, which exhibits 

 a similar relative position, has its base extended half -way down the inter- 

 space ; its strong transverse process extends outwards and forwards, and is 

 at first contracted, then expands both transversely and vertically, juost so in 

 the latter direction, and is twisted obliquely, so that the lower end is directed 

 downwards and forwards, and the upper and thicker end is bent obliquely 

 backwards, until it meets and becomes anchylosed to the anterior production 

 of the transverse process of the next vertebra behind : an elliptical space is 

 thus produced, the axis of which is nearly vertical, and into this space the 

 neui'al canal opens ; the nerve being transmitted over the middle of the body 

 of the vertebra, as in the sacrum of the Megalosaurus. 



The upper and inner part of the base of the broad, oblique transverse pro- 

 cess, or sacral rib, abuts against the base of the spinous process. There is 

 no appearance of accessory spines, such as the sacrum of the Megalosaurus 

 is complicated with. 



The following are admeasurements of the present portion of the sacrum of 



the HylcEOsaurus : — 



In. Lin. 

 Length of the body of the third vertebra ......:. 2 



Breadth of its articular end 2 



Breadth of its middle part 1 4 



Breadth of its inferior groove 4 



Length of the transverse process .1 10 



Antero-posterior diameter of the middle of process 4 



Vertical diameter of base of process 1 6 



Vertical diameter of expanded extremity 3 



From the lower part of centrum to the origin of the spinous process 2 6 

 The spines appeal- to be anchylosed into a continuous ridge. 

 The anterior surface of the transverse process appears undulated by wide 

 shallow depressions and intervening elevations. 



Caudal vertebra. — A proportion of the tail, to the extent of nearly six feet, 

 and including about twenty-six vertebrae, discovei-ed in a quarry in Tilgate 

 Forest in the year 1837? is preserved in the Mantellian Collection. The 

 transverse processes present almost Crocodilian proportions, in regard to their 

 length, at the anterior part of this series, and may be discerned, though dimi- 

 nished to mere rudiments, in the small terminal vertebrae of the series. In 

 the most perfect of the anterior vertebrae they are compressed vertically, but 

 with convex, not flattened sides, and rounded edges, presenting an elliptical 

 transverse section, and preserving the same breadth to their truncated extre- 

 mity : they extend outwards, and are slightly bent forwards : the breadth of 

 this vertebra between the extremities of the transverse processes is 11 inches. 

 The neurapophysis is curved forwards from the base of the transverse process 

 to form the anterior oblique process ; its length from the extremity of this 

 process to that of the posterior one is 3^ inches. The neurapophysis presents 

 a simple convex external surface to the base of the spine : the antero-poste- 

 rior extent of this process is two inches. The chevron bones are from four 

 to five inches in length near the base of the tail ; they may be distinguished, 

 like the transverse processes, by their convex external surface ; their base is 

 open, not confluent as in the Iguanodo7i, and articulated to two distinct tu- 

 bercles. Between these tubercles, which are placed at each end of the under 

 surface of the centrum, there is a longitudinal sulcus. The transverse pro- 

 cesses soon lose the slight anterior curve, stand straight out, decrease in 



