CIRCULATORY SVSTEIM. 3 73 



HEART. 



Form, Situatio)i, and Attachment. — It is of a conoid form. 

 Its base, turned uppermost, is opposed to the bodies of the 4th, 

 5th, and Gth dorsal vertebree, 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 tveight 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 bodif, 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 e\)\- 

 ihei^right and left, would more properly be described, in allusion 

 to the relative situation of then- cavities, as anterior and poste- 

 rior ; for the right auricle forms the upper andyb/e pait, 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 tiie 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 pink colour, are very uneven, when distended, 

 upon their surfaces, and are indented along their inferior borders; 

 whereas the ventricles are of a dnW red or deep flesh colour, are 

 smooth and even upon their surfaces, and of themselves compose 

 three-fourths of the organ. 



The right auricle, generally found full of blood after death, 



