28l 
mechanism of the spine. 
* 
membranes, it completely filled the canal, in every motion 
of which it must, in that case, participate. 
To afford additional support to the marrow which this 
loose state of membranes would leave very insecure, if en- 
closed in so delicate a tissue as the pia mater of the brain, 
this membrane, which may be considered as the proper tunic 
of the marrow, is greatly thickened, and partakes more of 
the characters of a fibrous membrane. 
The membranous band, which has been termed the liga- 
mentum denticulatum, appears to be superadded to restrain 
the lateral motions of the marrow, and to steady it in the 
canal. By these membranous processes, the marrow may 
not, improperly, be said to be lashed to the sides of the spinal 
sheath, in which, from the disproportion between them, it 
would otherwise be liable to perpetual variation of position, 
and pressure from the bony parietes. That a certain degree 
of freedom of motion between the membranes is essential to 
the due performance of the functions of the spinal marrow, 
is proved by the effect of accidents and disease. It would be 
out of place here, to bring forward a detail of particular 
cases, but I may mention briefly, that I have ascertained, by 
dissection, that the most distressing train of nervous symp- 
toms, and even complete paraplegia, may be produced by ad- 
hesions taking place between the membranes, and by effusion 
into the canal or theca. 
In conclusion I may observe, that this view of the subject 
tends to throw considerable light on the pathology of the 
spine, and assists in explaining a circumstance which I have 
repeatedly noticed in diseases affecting the vertebrae, namely, 
that the symptoms of irritation and inflammation of the spinal 
MDCCCXXII. O O 
