The heart is a cone-shaped muscular organ located within the
(1). Its apex rests on the (2), and its base is at the level
of the (3) rib. The coronary artenes that nourish the
myocardium arise from the (1). The coronary sinus empties
into the (5). Relative to the roles of the heart chambers, the
(6) are receiving chambers, whereas the (7) are
discharging chambers. The membrane that lines the heart and
also forms the valve ſaps is called the (8), The outermost
layer of the heart is called the _09_. The fluid that fills the
pericardial sac acts to decrease (10) during heart activity.
The heart muscle, or myocardium, is composed of a special-
ized type of muscle tissue called (11)