16 
FOSSIL REPTILIA OF THE 
lines is maintained through, nearly the whole of that length, in corresponding close 
contact with the contiguous spines. In the thirty-seventh vertebra (Tab. VII, 37) 
the length of the neural spine is five and a half inches ; it lias a little increased in thick- 
ness ; the fore-and-aft diameter continues the same. In the second dorsal the neural 
spine is six inches four lines in length, with a thickness of six lines. These dimensions 
are continued to the fifty-eighth vertebra, save that, in the posterior half of the dorsal 
series, the spines have less fore-and-aft breadth at their proximal third, and leave cor- 
respondingly wider intervals ; they are in contact at their more expanded distal 
portions. From the fifty-eighth vertebra they gradually decrease in length to the 
sixty-second, or sacral vertebra, showing a height of less than four inches, with a ter- 
minal fore-and-aft extent of two inches, and a thickness of six lines. They deerease 
in all dimensions as the caudals recede from the trunk, and most so in fore-and-aft 
extent, leaving wider interspaces ; by which character, with the higher position on the 
centrum, and anchylosed condition of the pleurapophyses, a caudal vertebra may be 
distinguished from a cervieal of similar size. The caudal centrums are also thicker in 
proportion to their length, and the under surfaee, if exposed, would doubtless also 
yield the character of the hsemapophysial pits. 
The dorsal diapophyses progressively increase from the first (Tab. VII, d i, 2, d), and 
attain, at the fifth dorsal vertebra (Tab. V, fig. 1), a length of two inches three lines 
along the upper border. The rib-surface is cut from above downward and inward, 
shortening the under extent of the process. A low ridge is continued from the pos- 
terior angle of the neurapophysis upon the back part of the diapophysis, which expands 
to the truncate articular surface. After the sixteenth dorsal the diapophyses gradu- 
ally shorten to the saeral vertebrae, where they have almost subsided. 
The zygapophyses in the neck (Tab. V, fig. 2, s, /) and greater part of the back 
are nearly horizontal, the anterior ones looking a little inward as well as upward, the 
posterior ones the reverse ; they are given off nearer the base of the neurapophysis 
than usual (compare Tab. V, fig. 2, s, s' with Tab. Ill, fig. 4, Plesiosaurus dolichodeirus, 
with Tab. X, fig. 1, PI. rostratus, and Tab. IV, fig. 1 1, ‘ Monogr.,’ 1862, Pl.Pernardi)-, 
towards the end of the back their aspect gradually changes; and, in the tail, the 
artieular surface becomes almost vertical ; that of the anterior ones, which are most 
developed and longest retained in the vertebral series, looking inward. The terminal 
articular surfaces of the centrum of the last dislocated caudal vertebrae are, as usual, 
more concave than in the neck. 
The development of the neural spines throughout the trunk and base of the neck 
is such as to impede infiection in the vertical direction. At the anterior half of the 
long and slender neck this bend would, indeed, take place in some degree ; but the 
greatest flexibility would be from side to side. The provision for the attachment of 
the vertebral muscles in the trunk is very great, indicative of corresponding power of 
regulating the movements and position of the body during the application of the 
