AND FAMILY DISPENSATORY. rer 
It is, both externally and internally, furrounded ‘with a {mooth membrane. "There 
§s-a quantity of fat about it, which covers its bafe and its apex, and ferves for lu- 
bricating it,’and for facilitating its motion. Its blood-veffels are of two kinds, 
common and proper; its common or peculiar veffels being the coronary arteries 
and ‘veins. The common veffels of the heart are two veins, called the vena cord, 
and the vena pullmonalis ; and two arteries, the pulmonary one and aorta. "The nerves 
of the heart are fmall, and arife from the par vagum and intercoftals : the turicles art 
two: There are alfo two cavities in‘the heart, called its ventricles : of thefe the 
right'is thinner and weaker in its circumference, but ufually much more eapat 
than: the left: it receives the blood from the vena cava and the right auricle, and 
delivers it into the pulmonary artery, to be carried to the lungs. The left ventricle 
is much ftronger aiid thicker in its fides ; but it is narrower and fimaller than’ the 
Tight = it receives the blood froin the pulmonary vein, and the left auricle, and ¢ ex. 
trades it’very forcibly into the aorta.’ The right ventricle is in the anterior part of 
the thorax ; fo that they might be called the anterior and pofterior ventricles, much 
more properly than the right and lefr. There are in the fides of both the ventricles 
“of the heart, and of both its auricles, feveral columne tarnte, or dacertali, with for- 
xows between them, {eming fo many fmall and diftiné& mufcles ; and, from the 
concourfe of the tendinous fibres of thefe’in the heart, there are formed peculiar 
membranes fituated at the orifices of the auricles of the heart: and there are alfo 
‘other columns of this kind, which run tranfverfély from one fide of the ventricles 
tothe other: thefe ferve partly to affift the contraétion of the heart in its ‘fyftole, 
land partly to prevent its too" great dilatation in its diaftole. The valvule of the 
heart are of three kinds, | 1.’ The ticw)pidales, thefe are three in humber, and are 
fituated at the ingrefs of the vena cava gn the right ventricle. 2. The mitrales ; 
thefe are two, and are fituated in the left ventricle at the ingrefs of the pulmonary 
vein: thefe ferve to hinder the ingrefS of the blood from the heart into the veins 
again, while they are conftridted. 3. The femilunar ones, thefe ‘are three, and are 
ficuated:at theorgan of the aofa and pulmonary artery, and ferve to prevent the 
seflux of the blood from them into the heart: thefe, for the fake of ftrength, ‘are 
fornithed with a number of flefhy fibres and fpheroidal corpufcles. ‘The orifices of 
‘theveins of Thebefius and Verheyen, in the hollows of the heart, are for carrying bac 
‘the blood from the fubttance of the heart to its cavities. The fibres of the he rf 
“are of a‘mufcular fubftance, and of a moft amazing fabric. Ri gkoe., Wor ria . 
no ftraight ones i inthe left ventricle; and, 2. fpiral ones, common to both s Se tr 
“and of two orders. “Phe ‘exterior ones run to the left, from the bafe of the 
othe ‘interior ones run to the right, and interfect the others ; and, whe 
they-clofely eanftringe the cavities of the heart, and rive out the slood. 
afi: B3.° Dée 
