268 O. C. Marsh—Vertebree of Recent Birds. 
moderately convex, while transversely it is strongly concave; 
thus presenting a near approach to the saddle-like articulation. 
None of the other known vertebrae of Ichthyornis possess this 
character. 
This highly specialized feature occurs at the first bend 
of the neck, and greatly facilitates motion in a vertical plane. 
f, now, we consider for a moment that the dominant motion 
the sacrum, if the same flexure was continued. 
Behind the axis, or where the vertical motion prevails, we 
find in modern birds no exception to the saddle articulation 10 
the whole cervical series. 
lateral flexure; or several vertebree ror be codssified, as in 
Accipiter and some other Raptores, in which a stiff back 1s 4 
positive advantage. 
