24 THE STRUCTURE AND LIFE OF BIRDS cuap, 
joints in a bird’s neck resemble two saddles laid 
crosswise one upon the other, so that the pommels 
of one face at right angles to those of the other, the 
upper saddle being, of course, upside down. In the 
bird’s neck the “ saddles” are so arranged that at the 
hinder end of each vertebra the pommels are at the 
top and bottom, while at the front end they are at 
the sides. Thus the two vertebra will slide over 
one another sideways, or up and down, in the same 
way that two saddles will slide when they are laid 
upon one another in the way which I have described. 
And the upright spines in a bird’s neck are small and 
far from one another, so that they do not hinder the 
movement (SP, fig. 2). 
The backbone of the bird has been so much modified 
for purposes of flying and walking that it presents a 
difficult study. The vertebral columns of reptiles and 
mammals are divided into well-defined regions—the 
regions of the neck, breast, loins, pelvis, and tail. In the 
bird, fusion or ankylosis has gone on to such an extent, 
and the pelvis has extended so far backwards and 
forwards, that it is a most perplexing problem how to 
map out the backbone. I shall not attempt this here. 
The subject does not seem to be of first-rate importance; 
in studying the views held by various great authorities, 
not very much of the principles of anatomy would be 
learnt, since it is admitted that there is no essential, no 
morphological difference, to use the technical term, be- 
tween a neck vertebra and a thoracic or breast vertebra. 
They are corresponding organs, in slightly different 
places and slightly modified, a breast vertebra being 
defined as one which has attached to it a rib that 
