42 
that the skull when attached to the vertebral column is 
directed markedly downwards (see fig. 17). 
The anterior notochordal space in most of the trunk 
vertebrae (except the atlas) is perceptibly deeper than the 
posterior, so that the notochordal canal is situated nearer 
the posterior than the anterior face of the centrum. This 
is more marked in some vertebre than in others. 
Atlas (figs. 10 and 17).—Body compressed from before 
backwards. Notochordal canal (V.C.) much nearer dorsal 
than ventral surface. Bears two large cartilage capped 
facets (C.F.) for articulating with the paroccipital con- 
dyles, of which the left is perceptibly larger than the 
right. The anterior face of the centrum also articulates 
with the single occipital condyle on the basi-occipital, the 
connection of the skull with the vertebral column by 
means of 3 condyles being therefore very strong. Unlike 
all the other vertebrae, except about the last 5, the neural 
arch of the centrum is only perforated by one foramen on 
each side for the second spinal nerve. There is no trans- 
verse process, and only one rib, which belongs to the series 
of accessory ribs or intermuscular bones (A.#.1), and is 
attached to its vertebra higher up than any of the others, 
articulating at the junction of the neural arch with the 
centrum (figs. 10, 17). As in all the other vertebre 
(although the tendency is faint in the posterior caudals), 
and as first described by Traquair, the atlas is markedly 
asymmetrical, the neural spine being directed towards the 
eyeless side. The asymmetry here is obviously an adapta- 
tion to the habit of the animal in lying on its eyeless side. 
Superficially this side is practically flat, whilst the ocular 
side is convex. The asymmetry of the vertebre, there- 
fore, tends to a flattening of the eyeless side and an arch- 
ing of the ocular side (ep. figs. 11 and 13). The neural 
spine itself is in the form of a rolled plate forming a hollow 
