On Motion in the lumbar division of the spine of birds, by George Oakley Fleming

                                perfect hinge like joint admitting of motion laterally. 
These joints have capsular ligaments and are lined 
by a synovial membrane. The formation of the 
articular processes of the lumbar vertebrae deserve 
attention in relation to the lateral movement of this 
part of the spinal column in birds, these articular 
surfaces on one vertebra being somewhat obliquely 
situated and looking forwards, which exactly oppose 
the articular surfaces of the processes of the adjoining 
vertebrae, which are also somewhat obliquely situated 
and looking backwards. These joints are also lined 
by a synovial membrane and surrounded by a capsular ligament. 
(See Plate 3. Figure 1 & 2: letter a, Plate 1, letter a, representing the articulation of these parts in the peacock) The 

and lumbar portions of the spine, which admit of no motion whatever, 
and where there is no variation in the diameter of the spinal 
canal.” Animal and Vegetable Physiology, considered with 
reference to Natural Theology. Bridgewater Treatise. Vol: 1, 
p. 564. 
“A Plan entirely different is followed in the vertebrae of the back 
and loins. For the purpose of insuring the proper action of the wings, the 
great object here is to prevent motion, and to give all possible strength 
and security; and accordingly the whole of this portion of the spine 
together with the sacrum is consolidated into one piece. All the pro-
cesses are largely developed and pass obliquely from one vertebra to 
the next, mutually locking them together; and in order most 
effectually to preclude the possibility of any flection, the spinous processes 
and sometimes even the bodies of the dorsal vertebrae are immoveably 
soldered together by ossific matter, so as to form one continuous bone.”