62 
LECTURES ON HORSES. 
elliptical or circulafr, according as circumstances require : a pro- 
perty that could not be given to the mechanical arch without ren- 
dering it unstable and detracting considerably from its strength. 
At the same time it is worthy of remark that, wherever there is any 
elasticity arising either from the materials of which the arch is 
composed, or from the nature of its construction, it is invariably 
found to possess, in consequence, increased powers of resistance. 
A happy elucidation of this is seen in the common violin, which, 
when strung up to concert pitch, has been calculated to be actually 
sustaining a force equal to eighty pounds ; under the pressure of 
which it would certainly break were it not for its arched form and 
the elasticity of the material (very old seasoned deal) of which it 
is made. 
From their mobility the arches of the spine not only derive the 
requisite elasticity, but likewise that self-regulating power which, 
under all changes, preserves their equilibration or undiminished 
strength. Dr. Hutton, in his “ Principles of Bridges,” tells us that 
the arch of equilibration, i. e. the one which is in equilibrium in all 
its constituent parts, is the only one which admits of a horizontal 
line across its top, and, in addition to being both graceful and con- 
venient, possesses the advantage of being made higher or lower 
at pleasure, with the same span or opening. He adds, that the 
elliptical form of arch approaches the nearest to that of equilibra- 
tion for strength and convenience. How strikingly and beautifully 
is all this verified in the fabric of the spine, and how wonderful it 
is that the structure should be capable of preserving its equilibra- 
tion under all the various changes of figure and space which its 
arcs must, in the movements of the animal, be continually under- 
going! Who but “ the Divine Architect of the Body” could have 
framed and finished such a piece of workmanship 1 
It must be manifest that the mechanical powers of the spine, 
regarded either as a fixed or moveable body, must be affected by 
its length: and that there exist considerable variations in the 
longitude of spines, must appear self-evident to any observer of 
horses — not that there are any additional bones in a spine of un- 
usual length ; but that the vertebrae are of larger size, and their 
bodies and intervening cartilages are thicker. Some horses have 
very long backs and necks ; some very short ones. Hardly any 
two have backs and necks of the same length; from all which 
result certain advantages and disadvantages. We will first con- 
sider the longitude of that part of the spine that forms the back, 
and in two points of view : — 1st, as it affects the support of weight; 
2dly, as it mechanically affects progression. 
Regarding the dorsal portion of the spine with its super-imposed 
burthen as a pole or lever supported in front by the fore limbs 
