662 
ANATOMY OF THE HORSE. 
ation, to sustain it in its reciprocal action with the lungs, pre¬ 
venting any undue collision, and to serve as a protecting fence to 
the organ. 
HEART. ‘ | ... 
Form , Situation , and Attachment .—It is of a conoid form. 
Its base, turned uppermost, is opposed to the bodies of the 4th, 
5th, and 6th dorsal vertebrae, from which it is suspended in its 
situation in the middle of the cavity of the thorax, by the at¬ 
tachments of the venous and arterial trunks immediately con¬ 
nected with it. Its apex hangs loose and unattached within the 
pericardiac cavity, pointing downwards and backwards, and is 
inclined to the left side. 
The weight of the heart is about six or seven pounds. 
Division , external and internal .—For the convenience of de¬ 
scription, we distinguish in the heart a base , a body , and an 
apex . 
It is also said to have two sides , each of which contains two 
cavities: the two superior cavities (from having been likened to 
the ears of a dog) have been denominated auricles; the two infe¬ 
rior have been named ventricles . Their boundaries are marked 
externally by deep excavations, which are filled with fat; the 
limits of the ventricles are likewise pointed out by furrows upon 
the body of the heart, containing fat, continuous in substance 
with that which is deposited above. This fat is more abundant 
in old than in young horses. 
The heart owes its smooth glossy aspect externally to its thin 
duplicature of pericardium, which is everywhere in such intimate 
adhesion with its surface, and so transparent, that its parietes 
are too plainly demonstrable through it to require that this mem¬ 
brane be stripped off. 
The sides of this organ, commonly distinguished by the epi¬ 
thets right and left , would more properly be described, in allusion 
to the relative situation of their cavities, as anterior and poste¬ 
rior; for the right auricle forms the upper and fore part, turning 
its apex to the left side; and the greatest part of the left auricle 
is apparent behind , though its apex is also turned to the left side, 
and is inclined downward. The ventricles, being situated under 
their respective auricles, face consequently, like them, forwards 
and backwards. Though the auricles are essentially the same in 
structure as the ventricles, they differ from those parts in exte¬ 
rior appearance, in bulk, and in the substance of their parietes: 
they are of a pale red colour, are very uneven, when distended, 
upon their surfaces, and are indented along their inferior borders; 
