20 THE STRUCTURE AND LIFE OF BIRDS chap. 



utmost importance. Otherwise, how could the head 

 be supported at the end of so long a neck ? But 

 muscles get tired with prolonged exertion, however 

 slight the exertion may be, and to provide against 

 this there are, between the spines of the vertebrae of 

 the neck (SP, fig. 2), elastic ligaments similar to that 

 which is so enormously developed in the horse's neck 

 to support his ponderous head. These ligaments hold 

 the neck in position when it forms an S. In the Swan 

 they are but slightly developed, hence perhaps the 

 ease with which he erects his neck straight as a flag- 

 staff. Even when there are ligaments to relieve the 

 muscles, the skull is the place where aeration of bones 

 is desirable if anywhere. Its great size compared with 

 that of the lizard, and, consequently, the great size of 

 the brain, I have already pointed out. The skull, too, 

 illustrates better than any other part of the skeleton 

 the tendency to ankylosis, or fusion of bones. Even 

 in a very young bird this has already proceeded a long 

 way. The skull seems to be made up of a shell of 

 bone almost without suture. It is really composed of 

 scores of different bones, the boundary lines between 

 which may be seen in the embryo. And how are these 

 to be studied ? It is possible to go through them and 

 learn them up as one does for an examination. But • 

 for such studies it is usually the imminence of the 

 examination, not the interest of the subject, which 

 supplies the stimulus. Without this stimulus, to a 

 mind that has not as yet the patience wanted for 

 scientific investigation — the patience to collect facts ? 

 even if the clue to them and the interest of them may 

 not be found tiii years after — there is something barren 



