266 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



prominence of a broad longitudinal ridge, equivalent to that 

 bearing the parapophysial surface in the cervical, above and 

 below which there is a deep concavity. The spinal canal has 

 a transversely oval outline, and enlarges considerably towards 

 each extremity. The length of the body is 4J inches. 



The median dorsal vertebrae are typical of the Igua- 

 nodon, several having been found connected with the extremi- 

 ties and other parts of the skeleton. There is a fine example 

 (Mantellian collection, 2160) on the lower shelf to the left of 

 the group of caudal vertebrae (see Diagram, p. 227) ; but I 

 have several larger and more perfect than any in the British 

 Museum. 



The centrum has the sides smooth, concave in their antero- 

 posterior diameter, and slightly convex in the opposite or ver- 

 tical direction ; the articular faces are nearly flat, or slightly 

 concave ; in some examples they are flat in front, and depressed 

 behind ; of an oval form vertically, and flattened laterally ; 

 the sides of the centrum converge towards each other below, 

 so as to impart a wedge-like shape to the inferior part in a 

 vertical section. The suture uniting the body to the neura- 

 pophysis is almost obliterated in the adult state. The neural 

 arch rises into a broad expansion, or platform, which is sup- 

 ported on each side by a strong buttress, or pillar, that 

 springs from the hinder and outer angle of the base of the 

 neurapophysis. The spinous process rises from the entire 

 median width of the neural platform, contracts as it ascends, 

 and inclines gently backwards. 



The articulating depression for the head of the rib is of an 

 elliptical form, and is situated on the side of the neural arch ; 

 in the anterior dorsals it is placed on the centrum. 



The anterior oblique processes are oval, and face each 

 other ; their upper margins are four inches apart : but their 

 inferior ones are separated only by a slight notch in front of 

 the spinous process ; they extend but little from the neural 

 platform. The hinder oblique processes are sent off from the 

 under and back part, and overhang the posterior surface of 

 the centrum ; their articulating facets are turned down- 

 wards, and outwards. The upper transverse process is very 

 strong, and of a trihedral form ; it is directed upwards and 

 outwards, with an inclination backwards from the sides of the 

 neural platform, and is supported by a diagonal buttress, or 



