i8s 
Mr. Home on the Nature of the 
ture corresponds with that of the whale ; in the three last, the 
central substance appears to be the most compact. Besides 
the structures already mentioned, there is in some animals 
one of a very different kind ; in the alligator the vertebras 
through the whole length of the spine, have regular joints 
between them, the surfaces are covered with articulating car- 
tilages ; and there is synovia and a capsular ligament. In the 
snake, there is a regular ball and socket joint between every 
two vertebrae ; so that the means employed for the motion of 
the back bone in different animals, comprehends almost every 
species of joint with which we are acquainted. 
Having mentioned a sufficient number of facts to point out 
the animals, in which the different structures of the interver- 
tebral substance are to be found, I have abstained from being 
more particular in my account ; as it would in no respect elu- 
cidate the principal object of the present communication. 
From the facts and observations which have been stated, it 
appears that the intervertebral substance of the human spine 
does not consist entirely of elastic ligament, dense in its tex- 
ture at the circumference, and becoming gradually softer to- 
wards the centre; but that the middle portion is composed of 
materials which render it very pliant, though not at all elas- 
tic, fitting it to keep the vertebrae at the proper distance from 
each other, so as to admit of the action of the lateral elastic 
ligaments. 
When this knowledge is applied to the treatment of cur- 
vatures of the spine, a complaint so commonly met with in 
young women, whose strength does not bear the necessary 
proportion to the growth of the body, it will show the great 
impropriety of overstretching the intervertebral ligaments. 
