OCR Text |
Show 1894.] IN THE BRITISH MUSEUM. 119 The cervical (Plate XV. figs. 2, 3, 4) is of the following dimensions :- cm. Length of centrum 4-1 Width between anterior ends of pre-zygapophyses . 2*5 Width between outer edges of post-zygapophyses.. 2*6 Diameter of neural canal 1*0 Longest diameter of anterior end of vertebrarterial canal 1*4 The centrum is much compressed from side to side in its middle portion, but widens out towards the ends. The articular surfaces are of the characteristic avian form; the anterior is wide from side to side and narrow from above downwards, owing to its upper and lower borders being deeply concave; the posterior is shghtly wider than high and all hs borders are concave, the lower deeply so. On the ventral surface of the centrum, about one third of its length from the anterior end, is a median hasma-pophysis, the front of which rises steeply, while its hinder border passes by a more gradual slope into a median ridge which runs back for about 1-5 cm. in the middle ventral line. There is no pneumatic fossa in the side of the centrum. The lateral portions of the neural arch are remarkably thin. The diapophyses and parapophyses are well developed, and, on the left side, the fused cervical rib is nearly complete, only its hinder portion being broken away. The vertebrarterial canal is very large, much larger, indeed, than the neural, a condition not occurring in the living Bacites or, to the same extent, in Dinornis. The interzygapophysial bar has behind and beneath it a pneumatic fossa, and above and in front of it on the dorsal surface, immediately behind the anterior zygapophyses, there is a still larger fossa into which several pneumatic foramina open. On the upper surface of the post-zygapophysis, near its outer hinder border, is a small tubercle (hyperapophysis), from which there runs forwards and inwards a ridge which increases in size as it goes; this does not meet its fellow of the opposite side to form a median neural spine, but is separated from it by a groove, which is shallow in front but deepens suddenly behind, forming a pit for the intervertebral ligament. The cervico-dorsal vertebra differs from the one just described in possessing a broader and less compressed centrum, into the sides of which open a pair of large pneumatic fossas. The arch also is more massive and the ridges running forward from the post-zygapophyses very much higher and broader; as in the cervical, however, they do not unite to form a median neural spine. The pneumatic fossas of the arch closely resemble those of the cervical vertebras. The parapophyses and diapophyses have smooth articular surfaces for the free rib. The smaller dorsal vertebras are very similar to the larger ones, and since the latter are the more complete they will be here described, though measurements of both will be given. |