326 PETRTFACTIONS AND THEIR TEACHINGS. CHAP. III. 



and has two diverging and distinct processes of attachment, as 

 in the crocodiles. 



The bodies of the middle caudals are longer, narrower, 

 sub-angular, and somewhat enlarged in the centre ; they are 

 2 1 inches long, and 1| in vertical diameter. The transverse 

 processes proceed from the centrum in these vertebrae, and 

 gradually become less, till they are lost in the terminal 

 caudals. The corresponding chevron bones are hatchet- 

 shaped ; the length, 1 1 inch, is equalled by the antero-pos- 

 terior diameter of the distal expansion of the bone ; the two 

 laminae unite at the proximal end, and form a distinct canal 

 for the passage of the blood-vessels. The terminal caudal 

 vertebrae are elongated, and have mere rudimentary pro- 

 cesses ; length of the body 2 inches, vertical diameter, f of 

 an inch. The chevron bone undergoes a corresponding 

 change ; its antero-posterior extent equals the length of the 

 vertebra, but its vertical dimension is only | of an inch : the 

 contiguous haemapophyses, therefore, meet in the centre of 

 the body of each vertebra, a mechanism which conferred great 

 strength and flexibility. 1 



The osteological characters here pointed out, show that 

 the tail of the Hylaeosaurus presented a striking contrast, 

 in its form and construction, to that of the Iguanodon. 

 Instead of being greatly developed in a vertical direction, 

 the tail was broad and flat at the base, and gradually 

 tapered off into a nearly cylindrical flexible chord, several 

 feet in length. 



TEETH OF THE HYL^IOSAURUS ? No known vestiges of the 

 cranium or jaws of this reptile have been discovered, nor any 

 teeth that can with certainty be ascribed to it. Never- 

 theless, in the same strata with the remains of the skeletons 

 previously described, there have been found several teeth of a 

 peculiar character, which do not belong to the other species 

 of reptiles whose remains are recognised in the same beds, 

 and may in all probability be referred to the genus under 

 consideration. These teeth are about If inch in height, 

 and commence at the base with a cylindrical shank, which 



1 See " Philos. Trans." 1849, PI. XXXII.: a lithograph, the natural 

 size, of the specimen in the British Museum which exhibits this part of 

 the spinal column of the Hylgeosaurus. 





