THE GIGANTIC LAND-TOETOISE OE EODEIGUEZ. 
57 
regards the relative lengths of the several segments of the cervical column. In nearly 
all the cervical vertebrae two forms may be distinguished, of which one is still more 
slender than the other; but, with this exception, there is a great uniformity of 
structure or want of variation. 
No portion of the atlas has been preserved. Of the second vertebra we have two 
specimens, both of young individuals. It is provided with a moderately high neural 
crest, extending along the whole length of the bone in one specimen, and being limited 
to the anterior half in the other. 
The third vertebra has a condyle in front and a glenoid cavity behind, and scarcely 
any indication of a median crest of its neural arch. 
The fourth vertebra is biconvex, with the centrum much compressed, and passing 
into a sharp haemal crest which runs along the whole of its length. There is no 
neural crest. 
The fifth vertebra has a glenoid cavity in front and a condyle behind ; a median 
neural ridge is slightly indicated, and, in very old individuals, accompanied by a pair of 
other ridges diverging in the direction of the posterior zygapophyses. The centrum is 
compressed into a sharp ridge, highest on the posterior half of its hsemal surface. 
There is a deep impression inwards and backwards of each of the anterior zygapo- 
physes. The first of the vertebrae, of which the measurements are given below, be- 
longed to an unusually large individual (Plate XI. figs, B). 
The sixth cervical vertebra (Plate XII. fig. B) has a glenoid cavity in front and a 
broad condyle behind, which, by a deep median notch, is divided into two lateral 
halves. Its dorsal surface is flat, without crest, whilst on its visceral surface a rather 
high crest is evenly continued along nearly the whole length of the vertebra. As men- 
tioned in the preliminary notice, Ann. & Mag. N. H. 1873, vol. xi. p. 397, this vertebra is 
distinguished by the perforation of the neural arch by a large ovate foramen {a) on each 
side, close to the anterior apophyses. There is no doubt that these two foramina are 
closed by membrane in fresh specimens, and are the result of the absorption of the 
osseous substance caused by the pressure of the posterior zygapophysis of the preceding 
vertebra when the neck is so much bent that the fifth and sixth vertebrae stand nearly 
at a right angle. I am confirmed in this view by the fact that the natural bend of 
the cervical column is strongest at this place, which is opposite to the front margin of 
the carapace. However, although a very deep impression is constantly found imme- 
diately behind the anterior zygapophyses, which are perpendicular to the longitudinal 
axis of the centrum, the actual perforation of the neural arch has not always taken 
place. It is absent in all the vertebrae of less than 55 millims. length; and out of 
twelve vertebrae above that size I found it to occur five times. 
The seventh^ biconcave vertebra (Plate XIII. fig. B), is distinguished from that of the 
Aldabra and Galapagos Tortoises by the entire absence of the high prominence on the 
dorsal surface of the neural arch. On the other hand, the median crest at the opposite 
I 
