450 PKOF. W. J. SOLLAS Ofl A NEW SPECIES OE PLESIO S A T7ETJS 



of a bracket (}), the middle point of the bracket standing for the 

 point of junction of the two constituent ridges. 



In the thirty-sixth (xxxvi) the lower end of the neural arch is 

 still more swollen, and has retreated further up the centrum ; it 

 more abruptly joins the costal ridge, which has become almost 

 straight, and more prominent ; it extends down the middle of the 

 centrum to within 0*65 inch of an oval nutritive foramen, which lies 

 on one side of the concealed middle line of the base of the centrum. 



(xxxvn) An abrupt change in the character of the costal ridge 

 takes place in the thirty-seventh vertebra ; it has become greatly 

 enlarged, to form a simple transverse process, which, curving down- 

 wards and backwards from the neural arch, ends in an oval facet, 

 looking obliquely backwards and downwards ; the lower edge of the 

 facet rests upon the centrum, the pedicel of the transverse process 

 having as yet only an upper and not an inferior margin. The rib 

 is no longer hatchet-shaped, but of the ordinary half-hoop form ; it 

 is nearly cylindrical down to 1*3 inch from the transverse process, 

 and then expands laterally so as to become somewhat triangular in 

 section ; the line along which this change takes place is marked by 

 a strong ridge, oblique to the axis of the rib. A transverse fracture 

 across the front of this vertebra and the overhanging posterior zyga- 

 pophyses of the preceding vertebra shows that the zygapophysial 

 facets are not horizontal (as one might have conjectured), but much 

 inclined, the posterior looking outwards and downwards, and the 

 anterior inwards and upwards. 



(xxxvin) The base of the transverse process of this vertebra ex- 

 tends a little more than halfway down the centrum ; the facet is 

 borne on a distinct pedicel, and looks a little less backwards than 

 that of the preceding vertebra. This I take to be the last cervical 

 vertebra, the transverse process of the next vertebra appearing to 

 arise wholly from the neural arch. I use the word "appearing" 

 definitely, since, in the absence of any well-defined neuro-central 

 suture, it is difficult to say certainly what the exact constitution of 

 the transverse process is. It is clear, however, that the process in 

 this vertebra extends a little below the dorsal half of the centrum ; 

 and this is presumptive evidence * that it is cervical ; while in the 

 next vertebra it does not, but is wholly confined to the dorsal half, 

 and thus should be the first dorsal. Moreover, owing to a difference 

 in the colour of the substance of the centrum and that of the neural 

 arch, the latter being black and the former brown, in this region of 

 the vertebral column, it is possible to detect in the transverse pro- 

 cess of the thirty-eighth vertebra bone contributed by the centrum ; 

 in the transverse process of the thirty-ninth no certain indication 

 of bone so contributed is to be found. The possession of hatchet- 

 shaped ribs was at one time included by Professor Huxley in the 

 definition of a cervical vertebra ; if this should be regarded as an essen- 

 tial character, then the vertebrae thirty-seven and thirty-eight would 



* " There is reason to believe that the neurapophyses do not extend upon the 

 bodies of the cervical vertebras beyond their dorsal half." — Huxley, on Plesio- 

 saurus Etheridgii, Quart. Journ. Geol. Soc. vol. xiv. p. 282 (footnote). 



