356 BRITISH FOSSIL REPTILES. 



sphenoid bone, the inner margins of which touch anteriorly and then recede as they 

 pass backwards, leaving a heart-shaped posterior nasal aperture, the apex of which is 

 turned forwards. The breadth of this aperture is 1 inch 3 lines : its posterior position 

 gives another character by which the present Dinosaur, and probably the larger 

 genera of the same order, resembled the Crocodiles more than the Lizards. 



The bodies of the vertebrae are shorter in proportion to their breadth than in the 

 Megalosaurus or Iguanodon. They have not so smooth and polished a surface as in 

 the Megalosaurus, nor are they so contracted in the middle, or so regularly rounded 

 below from side to side ; a few of the anterior vertebrte are somewhat flattened below, 

 so as to present an obscurely quadrate figure ; most of the anterior dorsals (PI. 35, 

 figs. 10 and 11) are more compressed and keel-shaped below; the sacral (PI. 36) and 

 many of the caudal vertebrae (PI. 41) are longitudinally sulcated at their under 

 surface. 



The structure of the atlas and axis cannot be discerned in the British Museum 

 specimen ; the second (conspicuous) cervical vertebra (PI. 35, 4)* has its sides sub- 

 compressed, its under surface rather flattened anteriorly, and the slight angular ridges 

 separating it from the concave lateral surfaces are produced anteriorly into two feebly 

 marked tubercles. The parapophyses, or inferior transverse processes, are developed 

 from each side of the anterior part of the body of the vertebra ; they are subcircular, 

 very slightly prominent, about 7 lines in diameter. 



In the fourth (conspicuous) vertebra (PI. 35, c)* a parapophysis is, also, 

 developed from each side of the anterior part of the body, with the costal surface 

 directed obliquely outwards and forwards. There is a small costal surface at the side 

 of the expanded posterior extremity of the same vertebra, against which a part of the 

 head of a rib abuts ; that and three of the succeeding ribs having their heads applied 

 over the interspace of two contiguous vertebrae, as nearly throughout the thoracic 

 region in Mammalia. 



The lateral compression of the centrum increases in the sixth (s) and seventh 

 (9) (conspicuous) vertebrae, in which the under surface forms an obtuse ridge; 

 in the eighth vertebra (10) this surface is broader and more rounded. In none of 

 these vertebrae is a process developed from the under surface, as in the hinder cervical 

 and anterior dorsal vertebrae of the Crocodiles ; and in none of them is the anterior 

 articular surface of ihe centrum convex, as in the Streptospondylus. 



The most striking character of the vertebrae of the Hylaeosaurus is the great 

 development of the neural arch and its processes. The anterior articular processes 

 extend (in the anterior dorsal and cervical vertebrae) over half the centrum next in 

 front, and a broad diapophysis (upper transverse process) is developed from the side 



* The Arabic numerals indicate the position which I believe the vertebrse to have had in the entire 

 series forming the back-bone of the Hylaeosaur. 



