LIASSIC FORMATIONS. 
25 
summit, which is bent backward. The dorsal vertebrae continue to increase in the 
length and size of the diapophyses, in the height of the neural spines, in the breadth 
and depth of the centrum, and, in a still greater degree, in the length of the ribs ; in 
every dimension, in short, except that of the length of the centrum, which, in the 
tenth dorsal, is 1 inch 10 lines, and in no dorsal vertebra exceeds 2 inches. The 
breadth of the centrum in the tenth dorsal is 3 inches ; the height, 2 inches 3 lines ; 
the articular surface is moderately hollow at the middle, and gently eonvex towards 
the periphery ; the neural spines gradually attain the height of 3| inches towards the 
end of the series, the fore-and-aft extent being about 1^ inch near the summit, which 
is more thickened and truncate than in the neck, measuring, in some of these vertebrae, 
9 lines in thickness. Both margins are concave at the lower half of the spine, and 
the intervals between those of different dorsal vertebrae average about three fourths 
of an inch at the narrower parts of the spines. The length of the diapophysis 
is about l^inch; it expands to its extremity, which is abruptly truncate, looking 
obliquely outward, backward, and a little downward ; it is flat, and rather rough, for 
ligamentous union with the rib ; subquadrate in form, averaging about an inch across. 
The ribs attain their greatest length from the twelfth to the fifteenth dorsal, where 
they are 1 foot 6 inches in length, with a simple expanded end, corresponding in shape 
and size with the diapophysial surface ; the body of the rib is subcylindrical, then sub- 
trihedral, and again subcylindrical in shape, about 6 lines in diameter at the narrower 
part, and gradually enlarging at the distal third to the truncate extremity, which was 
ligamentously connected with the sternal rib. Some of the longest ribs have suffered 
fracture, and some contortion at their middle slender part, in the course of the 
cosmical pressure which has spread them out flat ; but they retain much of their natural 
curvatures on each side the vertebral column. After the thirteenth, the ribs gradually 
decrease to a length of 3^ inches, in the last vertebra, in which the rib articulates 
wholly with the diapophysis (twenty-second dorsal), the breadth of this rib is 5 lines. 
Where the rib begins again to descend from the centrum, it continues to decrease in 
length in the flrst and second, in the latter of which it begins to gain in thickness. In the 
forty-ninth vertebra, counting from the skull, which vertebra I have indicated (Tab. IX, 
s) as the first sacral, the rib is 2 inches 6 lines in length, and 9 lines in least diameter ; 
its head is partly buried in the matrix, but the articular surface next the vertebra from 
which it is detached is 2 inches in vertical and I inch in longitudinal diameter, and 
the surface projects below, from the centrum, as it does above, from the neural arch. 
The borders of the terminal articular surfaces of the centrum are thicker and rougher 
than those of the dorsal or caudal vertebrae, indicating a stronger connection between 
the vertebrae from which the pelvic arch was suspended. The rib of the second sacral 
is straight, 2| inches in length, and 13 lines in the smallest diameter. 
In the caudal vertebrae the neural spines gradually decrease in length, but more so 
in antero-posterior breadth, being longer, and with wider intervals at the basal half of 
4 
