MUE^NOSAUfiUS. 



95 



the centre is usually marked by a small dimple or pit indicating the spot where the 

 notochord was originally, situated. The sides of the centra beneath the bases of 

 the neural arch are concave both from before backwards and from above downwards. 

 The ventro-lateral regions of the centra are occupied by the rather prominent facets [r.f.) 

 for the cervical ribs. The shape of these surfaces differs in the different species : in 

 Murcenosauriis leedsi there is a prominent longitudinal ridge or fold immediately above 



Test-fisr. 51. 



Posterior cervical vertebrse (? thirty-fourth and thirty- fifth) of Murcenosaurus durobrivensls: 

 A, from left side ; B, from back. (R. 2863, f nat. size.) 



a.z., anterior zygapophysis ; n.c, neural canal; n.s., neural spine; ji.z., posterior zygapoph5"sis ; r., ridge on 

 inner face of neural arch ; r.f., facet for cervical rib ; s., neuro-central suture. 



the rib-facet (PI. IV. figs. 2-4). At about the fortieth vertebra the rib-facets begin to 

 rise on the sides of the centrum, and on the forty-fourth and the next one or two 

 vertebrse the facets are borne partly on the arch and partly on the centrum ; the 



