MUE^NOSAUEUS. 97 



The pedicles of the neural arches unite with large diamond-shaped facets which 

 extend nearly the whole length of the centra. In the cervical region, as in the rest of 

 the vertebral column, the neural arch maj' or may not fuse with the centrum, its 

 freedom or otherwise being apparently dependent entirely on the age of the individual. 

 In the type specimen of M^irwnosaurus leedsi the fusion is complete, while in a much 

 larger skeleton, to which Lydekker gave the name Cimoliosaurus durohrivensis, the 

 arches are all free (text-figs. 50-52), so that probably when full-grown this species 

 attained a much greater size than Murcenosauriis leedsi. Above their base the pedicles 

 narrow somewhat, but then widen out to the zygapophyses. Of these the anterior (a.z.) 

 are roughly oval in outline and their articular faces are flat or, in the hinder part of 

 the neck, concave from side to side ; as usual they look upwards and inwards ; the 

 posterior (j)^-) are similar in outline and are flat or somewhat convex from side to side, 

 and look outwards and downwards. Both the anterior and posterior zygapophyses 

 project considerably beyond the level of the articular ends of the centrum ; the 

 posterior to the greater extent. In about the anterior nineteen vertebrae a ridge runs 

 backwards from the outer edge of the anterior zygapophysis (text-fig. 50, A) and 

 posteriorly becomes continuous with the outer border of the posterior zygapophysis ; 

 in this region the neural spine {n.s.) rises from the middle of the surface bounded by 

 these ridges, which in the posterior cervicals becomes less and less developed till they 

 disappear, and the outer surfaces of the pedicles pass without interruption into the 

 sides of the neural spine. In the anterior portion of the cervical region (text-fig. 50) 

 the strongly compressed neural spines (n.s.) are low and confined to the posterior half 

 of the arch, but further back they become very high (PI. VI. fig. 4; text-fig. 51) and 

 widen out towards their base, so as to extend forwards between the anterior zygapophyses ; 

 their anterior border is concave, the posterior convex, and their summits, which are 

 abruptly truncated about at right angles to their long axis, are occupied by roughened 

 surfaces, which in life were no doubt tipped with cartilage. In the pectoral vertebras 

 (text-fig. 52) the centra and the neural arches are, on the whole, similar to the posterior 

 cervicals, except that the rib-articulation has passed upwards and is situated in part on 

 tlie centrum and in part on a short stout transverse process arising from the lower 

 part of the pedicle. This process becomes more and more prominent and rises on the 

 arch till on about the 46th vertebra, which may be regarded as the first dorsal, where 

 it alone bears the articulation for the rib. 



The articular surfaces of the centra of the dorsal vertebrae (PI. IV. fig. 5 ; PL V. fig. 5 ; 

 text-figs. 53-55) are nearly circular in outline, there being only a slight concavity 

 beneath the neural canal ; they are nearly flat, with a small papilla having a pit at its 

 summit, in their centre, and they are separated from the lateral and ventral surfaces of 

 the centrum by a sharp and clearly-defined edge. The ventral surface is smooth and 

 evenly convex from side to side ; the lateral surfaces beneath the facets for union with 

 the neural arch are somewhat concave and are perforated by large nutritive foramina. 







