LECTURES ON HORSES. 
605 
support or sustain the fore half of the body, and head and neck, and 
not to do much work in progression. I said before, and I repeat 
here, that as muscles are worked or exercised, so do they become 
large or powerful; and this, independently of original formation, will 
go far to account for their increased size in the hind as compared with 
the fore quarters, as well as for their largeness or plumpness in ani- 
mals in condition, and for their smallness or flabbiness in such as 
are out of condition. View the race-horse brought to the starting 
post in condition to run ; mark his beautiful satiny skin, elevated 
into prominences by the muscles underneath, which appear dis- 
tinct enough through it almost to admit of anatomical demonstra- 
tion : then feel his muscles, grasp his crest and shake his neck, 
and mark how firm and hard his flesh is, and how whipcordy 
and clear his sinews have through training become ; in fine, what 
a totally different creature he is from what he was before being 
put into condition to race. 
The Structure of Muscles is fibrous. So many packets of 
fleshy fibres, constituting in reality so many lesser muscles, dis- 
posed in parallel lines, and united together into one mass of flesh, 
form a distinct and separate muscle. But these packets are divisi- 
ble into smaller packets, and these again are resolvable into fibres 
of a still smaller description ; and of what the ultimate or primi- 
tive fibres consist, or what their true nature may be, microscopical 
observers are hardly yet agreed, some contending that they are 
tubular, others that they are beaded filaments. Be which or 
what they may, during life they possess the power of contracting 
or shortening themselves; and through this vital property of con- 
traction it is that all the motions and movements of the body are 
effected. The order or stimulus for muscular contraction is given 
by the brain, and conveyed to them through the medium of the 
nerves ; and the action proves feeble or forcible, according to the 
nature of the order, or the amount of nervous energy emitted into 
the muscle. What muscular contraction is, and how the phenomenon 
is effected, remains, after a host of minute and searching inqui- 
ries, still problematic : we know little more about it than that it is 
present with life and absent in death, and that, therefore, it is not 
dependent on elasticity or any abstract physical force. 
The Tendons or sinews with which most muscles are provided, 
and which are different altogether in their appearance (being white) 
and their texture from the muscles themselves, possess no power of 
contraction, neither are they elastic : they can neither shorten nor 
elongate. They are, in fact, simple cords connecting the mus- 
cles with such parts as they are designed to put in motion, and, 
being so much smaller than the muscles themselves, are on that 
account capable of being intruded into the composition of parts, 
