24 THE STRUCTURE AND LIFE OF BIRDS CHAP. 



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 vertebrae 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 



