3 78 
Mr. Home on the Nature of the 
the two contiguous vertebrae. When the liquid is evacuated, 
the elasticity of the lateral ligaments brings the ends of the 
vertebrae within an inch and half of each other ; in this state 
the inner layers of the ligaments, which are less firm in tex- 
ture than the outer, project into the cavity, and may be 
mistaken for a part of its natural contents ; this portion when 
soaked in water swells out to a considerable size, the water 
readily insinuating itself between the membranous layers of 
which it is composed. 
The whole thickness of the lateral ligaments is about one 
inch, the external half of which is compact and elastic, the 
other appears to possess a very slight degree, of elasticity. 
The appearance of the joint is shewn in the annexed drawing, 
and an account of the analysis of the fluid by Mr. W. Brande 
forms a postscript to this paper. Every part of the mecha- 
nism is formed upon so large a scale, that it is rendered con- 
spicuous, and nothing is left to doubt or conjecture ; the nature 
of the joint is different from every other that is met with in 
animal bodies, and there are many circumstances respecting 
it, which render it uncertain whether human ingenuity can 
ever make any resemblance to it, that can be applied to the 
purposes of mechanics. 
These would have been sufficient grounds for bringing this 
subject before the Society ; but there are others of still greater 
importance which have induced me to make it a separate 
communication ; it enables us to explain the general principle 
upon which all intervertebral joints are formed, which has 
been hitherto but imperfectly understood. With this view, I 
will first describe the principle upon which this particular joint 
is formed, and then shew the resemblance that it bears to 
