INTERCOSTAL MUSCLES—FORM OF THE CHEST. 547 
jointed attachment to the spine, there being no tubercle by which 
they are tied down to the transverse process; and, their attach¬ 
ment being looser to the cartilages of the ribs before them, their 
action is freest of all. Therefore, if you will observe the thorax 
of the horse even in ordinary breathing, and more particularly 
when the respiration is quickened, you will perceive that there 
is far more heaving and falling of the ribs posteriorly than an¬ 
teriorly. 
Comparison between the Intercostals and the Diaphragm. —The 
ribs, then, while they protect the important viscera of the thorax 
from injury, are powerful agents in expanding and contracting 
the chest in the alternate inspiration and expiration of air. In 
what proportion they discharge the labour of respiration, is a dis¬ 
puted question, and into the consideration of which we are scarcely 
qualified to enter, until we know something of the respiratory 
muscle, par excellence —the diaphragm. Thus far, however, we 
may say, that they are not inactive in natural respiration, although 
they certainly then act only a secondary part; but in hurried 
respiration, and when the demand forarterialized blood is increased 
by violent exertion, they are valuable and powerful auxiliaries; 
while experience teaches us that the animal is at his ease or 
distressed, galloping pleasantly on or blown, laboriously and pain¬ 
fully heaving, just in proportion as the intercostals can then assist, 
or just as the state of the lungs or the formation of the chest will 
enable them to act with vigour and effect. 
The best Form of the Chest. —Then, gentlemen, this leads us to 
a very important consideration,—the most advantageous form of 
the chest for the proper discharge of the natural or extraordinary 
functions of the thoracic viscera. The contents of the chest are the 
lungs and the heart; the first to render theblood nutrient and sti¬ 
mulating; to give or restore to it that vitality which will enable it 
to support every part of the frame in the discharge of its function, 
and devoid of which the beautiful and complicated machine is at 
once inert, dead, and still, for it is insensible to nervous stimulus: 
and the second to convey this purified, arterialized, vital blood to 
every part of the frame. Then, in order to produce and to con¬ 
vey a sufficient quantity of blood to the various parts that are 
to be nourished, or to which the power of contractility is to be 
given, these organs must be large. If it amount not to hyper¬ 
trophy, the larger the heart and the larger the lungs, the more 
rapid the process of nutrition, the more perfect the discharge of 
every animal function. 
The Circular Chest. —Then it would appear, that that animal 
will be fattest and most valuable whose chest is most capacious 
in proportion to his size; for, remembering what I have said, 
