20 PEOF. T. JEFFEEY PAEKEE ON THE 



The Vertebrae. 



These, like the other parts of the skeleton, are extremely fragile, so much so that 

 the majority of the neural spines were found, on the removal of the flesh, to be broken, 

 although the utmost care was used in cleaning them. 



The vertebral centra (figs. 22-24) are deeply amphicoelous, and may be described as 

 consisting of two cones (fig. 23) of wonderfully thin papery bone, united apex tn apex, 

 and bound together externally by a larger or smaller number of longitudinal bony 

 plates (figs. 22 and 24), radiating outwards from the long axis of the centrum. Of 

 these radiating lamelhe, as they may conveniently be called, the dorsalmost on each 

 side is vertical, projects beyond the general level of the vertebra, and forms a neural 

 plate (n.pl), from which, usually near the middle of the vertebra, a comparatively 

 slender neural process {n.pr) is given off'. This latter, uniting with its fellow of the 

 opposite side, forms the neural arch, from which an extremely slender neural spine 

 {n.s) passes usually vertically upwards. Similarly the ventralmost lamella of each side 

 is vertical, and in all but the first twenty vertebrae projects beyond the general level of 

 the centrum, forming a hcemal plate {h.pl), from which a hcenial process (hpr) is given 

 off. It will be evident from this description that the neural plate and process together 

 constitute the neurapophysis of the vertebra, the haemal plate and process its hsem- 

 apophysis. In no case do the latter unite to form a haemal arch. The radiating 

 lamellae on the lateral surfaces of the centra (r) usually end flush with its general 

 surface and form mere strengthening ridges. 



The long wedge-shaped spaces between these lamellae are partly filled up with the 

 remains of the original cartilage of the vertebra (coloured purple in figs. 23, 24), 

 outside which is a thick layer of remarkably tough fibrous tissue (coloured blue), the 

 presence of which made the cleaning of the centra a very tedious and difficult task. 



Perhaps the most striking point about the vertebrae is the gradual increase in length 

 of the centra from before backwards (see fig. 5). The centrum of the first or atlas 

 (fig. 20, <?. 1), is a mere flat disk, not more than ^^ inch from front to back; in 

 the second vertebra {c. 2) the antero-posterior measurement is increased to ■§■ inch, 

 in the third (c. 3) to f inch, in the seventh to | inch, in the twenty-second to I inch, 

 in the fiftieth to 1^ inch, in the eightieth to 2 inches, in the ninetieth to 3 inches, and 

 in the ninety-second (fig. 2-5, c. 92) to 4 inches. The last or ninety-third vertebra 

 (fig. 25, c. 93) is a little under 2^ inches long; but as I shall point out, it is probably 

 to be considered as representing only the anterior half of a vertebra, so that the 

 exception in its case is only apparent. 



The atlas (fig. 20, c. 1, n.s. 1, trp. 1 ; fig. 21) has a thin discoidal centrum, 

 presenting on its anterior face three facets corresponding with those of the occipital 

 condyle : its arch is the largest, and its spine the stoutest of the whole series ; the 

 spine also is shorter than any but those of the last three or four vertebrae — the entire 

 height of the atlas being a little under 2 inches — and is markedly inclined forwards. 

 On each side at the junction of the neural arch with the centrum, is given oS a long. 



