96 MAEINE EEPTILES OF THE OXFORD CLAY. 



ventral surface in the third cervical (first postaxial) is flattened or even slightly 

 concave from side to side between the bases of the parapophyses {pp.), but in the 

 more posterior vertebrae the ventral face is convex from side to side. There is no 

 hypapophysis. The parapophyses (pp.) are short stout processes, compressed from 

 above downwards and terminating in an oval concave surface for articulation with the 

 head of the rib ; the long axis of this surface is horizontal. In the anterior cervicals 

 they are situated somewhat nearer the anterior than the posterior end of the centrum 

 and are low down, so that they may project below the level of the centrum. Followed 

 back in the series they pass upwards on to the sides of the centrum and, in Steneosaurus 

 leedsi at any rate, become about equidistant from the anterior and posterior ends ; at 

 the same time they become rounder in section and their articular ends convex. In the 

 tenth cervical the parapophyses are separated from the diapophyses (dp.) by a notch 

 only, and in the first dorsal they arise with the diapophyses from a common base 

 borne on the neural arch. At their base the cervical parapophyses are connected 

 with the anterior edge of the centrum by a ridge, on their posterior side they arise 

 abruptly. 



The neural arch in the cervical region differs in the different species in several 

 respects, particularly in the height and width of the neural spine (n.sp.). In all, the 

 pedicles of the arch rise from long bases which extend the whole length of the 

 centrum, and may even form a very small part of the terminal articular surfaces. 

 Above their base, the borders of the pedicles are concave, both in front and behind. 

 Close to the neuro-central suture, which in old animals may be obliterated, are the 

 prominent diapophyses (dp.), which are oval in section, the long axis being horizontal. 

 These processes terminate in a slightly concave, fiat, or slightly convex facet for union 

 with the tubercle of the rib. They are directed downwards and shift backwards as 

 they are followed back in the series, so that in the posterior cervicals they are situated 

 a little behind the parapophyses. The large anterior zygapophyses (a.z.) project 

 considerably in front of the anterior end of the centrum ; their outer surface is convex 

 and is connected by a slight ridge with the base of the diapophysis ; in some cases 

 (e. g., St. leedsi, text-fig. 3-5, A) there may be a low ridge running from thence to the 

 outer edge of the posterior zygapophysis (p.z.) ; the articular surfaces are oval, very 

 slightly concave, and inclined to one another at an acute angle. The posterior 

 zygapophyses are borne on the posterior margin of the arch, the hinder edge of the 

 neural spine (text-fig. 35, B) passing down into a deep groove between their bases ; 

 the articular facets are flat or slightly concave and are inclined to one another at an 

 acute angle. The neural spines (n.sp.), as above noted, differ somewhat in form in 

 the different species. They incline a little backwards, especially in the posterior 

 cervicals. Their anterior border is thin and sharp, the posterior thickened and 

 roughened ; the truncated upper end is also roughened. The neural canal seems to 

 be relatively small. 



