The thick middle, muscular layer of the heart is the
a. endocardium
b. myocardium
c. tricardium
d. pericardium

The correct answer for the blank is-

b. myocardium.

Explanation:

Mycardium is considered as thick layer of striated, involuntary heart muscle that lies between the outer and the inner layer. The contraction of these muscles allows the pumping of blood to transport oxygen throughout body. In return, deoxygenated blood is sent to lungs from different organs.

Thus, option b) is the right answer.