H. G. SEELEY ON THE AXIS OP A WEALDEN DINOSAUR. 



461 



32. On the Axis of a Dinosaur from the Wealden of Brook in the 

 Isle of Wight, probably referable to the Iguanodon. By Harry 

 Govier Seeley, Esq., F.L.S., F.G.S., Professor of Physical Geo- 

 graphy in Bedford College, London. (Read May 26, 1876.) 



This vertebra was collected for the Woodwardian Museum of the 

 University of Cambridge by Mr. Henry Keeping, and catalogued in 

 my ' Index to the Aves, Ornithosauria, and Reptilia ' (p. 81) as the 

 axis of a Dinosaur. The specimen is perfect, and but very slightly 

 crushed from side to side. It measures 3| inches in length, from 

 the termination of the dentata to the posterior articular face of the 

 centrum. The vertebra has a small neural arch, and measures 3| 

 inches from the base of the centrum to the top of the neural 

 spine. 



The centrum is depressed, and anteriorly measures 1|- inch deep 

 from the neural canal to the base, and is 2 J inches wide over the 

 articular surface. This surface, below the dentata, is nearly vertical 

 (fig. l,a), and forms more than a quarter of a circle (fig. 2, a). In 

 the middle of the base of the centrum a wedge -bone ossification is 

 anchylosed, as in birds (fig. 2, a), and projects forward for about a 



Fig. 



1. — Axis of a Dinosaur from the Wealden of BrooTc. 

 (Side view. Half natural size.) 



a. Anterior articular surface, b. Articular band. c. Non-articular surface. 

 d. Dentata. e. Posterior articular surface. /. Anterior zygapophysis. 

 g. Diapophysis. h. Parapophysis. i. Neural ridge. /. Posterior zygapo- 

 physis. 



quarter of an inch. The vertical articular surface has its superior 

 (or interior) outline nearly parallel to the circumference of the bone 

 (fig. 2), and is rather more than | inch deep. Confluent with this 

 area, and between it and the underside of the dentata, which it 

 occupies for half an inch, is an articular band margined by a some- 

 what sinuous anterior border (fig. 1, b), which is J inch wide in the 



