The Framework of the Bird 79 
lungs, and other organs. Look at the two neck-bones of 
the ostrich in Fig. 47, where in addition to the central 
aperture, through which the spinal nerve-cord passes, two 
other openings will be seen, one on each side. Through 
these the vertebral arteries carry their burden of pure 
blood. The outer wall of this bony canal, extending up 
the whole length of the neck, is formed principally by 
what is left of the ribs which were once long and free, 
like their fellows farther down the back. Though re- 
duced to a tiny fragmentary arc of bone, yet they still 
perform a protecting function. 
In Archeopteryx (Fig. 5) there existed well-developed 
abdominal ribs, exactly like those found in crocodiles 
and other reptiles. In no living bird, however, are these 
found. 
Breast-bone 
The lower portions of the true ribs of our chicken 
are separate pieces of bone, slanting in a forward direc- 
tion and attached by a movable joint to the upper parts. 
These end close together along the sides of the large 
breast-bone, or sternum as it is called. In fact the origin 
of the sternum can be traced to the fused ends of these 
ribs, and in the sternum of an immature ostrich (Fig. 
58) the line of juncture between the two lateral halves is 
still distinct or even open. To the edge of this bone, 
nearest the head, two column-like shoulder-bones are 
attached, and in some birds the wish-bone is also joined 
to it (Fig. 1038). 
The sternum is one of the largest single bones in 
