Jan., 1892. 
DRAGONS OF THE PRIME. 
3 
to the pelvic bones ' they, by their action, pull the binder 
part of the vertebral column downwards from a more oblique 
to a less oblique position with regard to a vertical line passing 
through the axis of rotation, and,, consequently, raise the fore 
part of the vertebral column and of the body. The whole 
weight, therefore, of the fore part of the body is supported by 
these muscles, and the strain on the pelvis is very great, so that 
it would be torn away from the vertebral column were it not 
firmly attached to the same. This firm attachment of the 
pelvis to the vertebral column is effected as follows: the 
ilium extends forwards as well as backwards, and for its whole 
length, which, proportionally, is much greater than in the 
crocodile, is actually ossified into one piece with the vertebral 
column. Moreover, the ischium, which in the crocodile is only 
loosely attached to one end of the ilium, in most birds is turned 
backwards parallel to the backward extension of the latter, 
and united into one piece with it. So, too, the pubis, instead 
of extending forwards as in the crocodile, runs backwards also 
parallel to the ischium. The ischium, the ilium, and the 
hinder part of the vertebral column, then are all united 
together and form a single piece of bone. By this backward 
position of the ischium, and union with the bones just 
mentioned, two objects are gained :— 
(1.)—The ischium becomes firmly fixed, so as to afford a 
rigid surface for the attachment of the muscles which pass 
from it to the bones of the hind legs and keep the body semi- 
erect, and (2) a mechanical advantage is given to those 
muscles over that which they would possess were the ischium 
less oblique. 
For if the ischium (Fig. 3) is in the position FI, and a 
muscle is attached from the femur to it at a, then the 
available power at right angles to the body, which is the 
effective force in balancing the latter, will act at a distance 
Fa' from the fulcrum F ; if the ischium be in the position FI' 
and the muscle be attached at b, so that the distance Fb 
is equal to the distance Fa, then the distance from the 
fulcrum is greater, and, the force being the same as before, 
the movement obtained is greater—in other words, the 
muscle has greater power. The same holds for the muscles 
attached to the tibia. 
Another difference between the bird and the crocodile is 
that while the former walks on its toes , the latter walks on the 
soles of its feet. 
Now, the Dinosaurs are especially interesting, because 
some of them are like typical reptiles, and walk on all four 
legs ; in others, the front limbs are so much shorter than the 
