66 
THE EACES OF THE GALAPAGOS. 
rising in a posture of defence. This slenderness of the neck is not due to an increase 
in the number of vertebrae (which is constant in Tortoises as in Mammals, and limited 
to eight), but to their elongated shape. In T. elephantopus they are not quite so 
slender as in T. vosmceri, but much more so than in the species from Aldabra. Also 
the spinal canal is narrower than in this latter round-headed form. The crests of the 
dorsal as well as those of the haemal surface are well developed, and sometimes accompanied 
by low additional crests. All the articular processes diverge comparatively but little ; 
and those which in the Aldabra species are nearly perpendicular to the longitudinal 
axis of the vertebrae, are oblique and much depressed in T. elephantojncs. 
In the atlas (Plate XLVI. fig. A) the lateral portion of the neural arch (column) is 
veiy much constricted, not broader than the zygapophysis, which is elongate and con- 
siderably longer than that part of the bone which forms the roof of the arch. The 
centrum (odontoid process) (a) is a rhombohedral body. 
In the second vertebra the neural arch is remarkably compressed and elevated, also 
provided with a high neural crest. The third has a condyle in front, and a glenoid 
cavity behind. The fourth is biconvex. Thejifth (Plate XLVI. fig. C) has a glenoid 
cavity in front and a condyle behind ; its median neural crest is low, and accompanied 
on each side by two other crests, which diverge in the direction of the posterior zyga- 
pophyses. The sixth (Plate XLVI. fig. D) has a glenoid cavity in front and a condyle 
behind ; its dorsal surface is flat, without crest, whilst on its visceral surface a low crest 
is evenly continued along nearly the whole length of the vertebra. The seventh (biconcave) 
vertebra (Plate XLVII. fig. B) is distinguished by the high crest on its dorsal and vis- 
ceral surfaces ; in the middle of the vertebra the neural crest is split into two branches, 
diverging in the direction of the zygapophyses and leaving a deep triangular recess 
between them. The point of divergence forms a kind of summit («) to this vertebra. 
The neural arch is deeply hollowed out [b) inwards of and behind each anterior zyga- 
pophysis to receive the zygapophysis of the preceding vertebra ; but no perforation of 
the bone takes place as in the extinct species of Rodriguez. The eighth vertebra, with 
its bipartite anterior and single posterior condyle, and with its expanded hamate poste- 
rior zygapophysis, does not differ from that of the Aldabra species. 
The measurements of the second to seventh cervical vertebrae are as follows : — 
2iid. 
3rd. 
4th. 
5th. 
6th. 
7th. 
miUiin. 
miUim. millim. millim. 
miUim. 
millim 
55 
67 
85 
83 
85 
74 
Depth of centrum in the middle 
34 
28 
27 
27 
28 
53 
Horizontal width of middle of centrum 
15 
17 
18 
20 
29 
27 
15 
20 
19 
Width of anterior glenoid cavity 
30 
34 
40 
27 
32 
37 
19 
20 
43 
Distance of outer margins of anterior zygapophyses. 
. 23 
34 
35 
38 
40 
38 
Distance of outer margins of posterior zygapophyses. 
.. 25 
26 
28 
30 
29 
46 
