Robert W. Lovett - 459 
4. The backbone of a cat followed the same rule under the same con- 
ditions. 
5. The spinal column of a human cadaver with ribs attached but with 
the sternum removed when bent forward to the left, twisted in the same 
way as the flexible rods described above and could not be made to twist in 
any other way when bent forward to the left. 
6. The spine of the living model, bent in this way, twisted in the same 
way and when bent forward to the left could be made to twist in no other 
way. 
The following experiments in twisting were then made: 
(1). A quadrilateral strip of rubber was fixed at its lower end and bent 
forward away from the observer and then twisted at its upper end with its 
front surface to the left. In its upper two thirds appeared a lateral curve 
to the right as seen by the observer from the median plane behind. 
(2). A similar strip of lead behaved in the same way under the same 
conditions and it was noticeable that the lower third or quarter of the 
strip did not share appreciably in either the twisting or the side bend 
when the force was applied to its upper free end. 
(3). The backbone of the human cadaver, fastened in a vise at its 
lower end, and twisted by its upper end, showed a similar lateral bend, 
beginning when fairly erect in the dorso lumbar region. 
(4). The spine of the living model in active and passive twisting 
showed a similar curve to the same side under the same conditions. 
Here then were certain tangible facts to be looked into. The sugges- 
tion from the above mentioned experiments is that in its association of 
side bending and twisting, the human spine follows certain more general 
laws than are to be formulated by a study of its especial structure, in 
short that its general behavior is governed by the laws which would con- 
trol any flexible rod of similar shape, size, and elasticity. 
The history of the spine in its evolution is of interest. In the Cyclos- 
tomata the vertebral column consists of a non segmented homogeneous 
cartilaginous rod. Articular processes first appear in the Rays and 
Teleostei. The backbone of the lower fishes consists of a series of bony 
discs bound together by elastic intervertebral discs. It would seem from 
the history of the spine as if articular processes developed concomitantly 
with the elaboration of structure, as if they were incidental to its use 
rather than factors determining of themselves its types of motion. Jn 
the human spine, from this point of view, they would be regarded rather 
as helping it to carry out its functions as a flexible rod than as causes of 
its particular movements. 
An experiment was then undertaken to determine whether the articular 
