Final answer:
The broad sheet of connective tissue that attaches the coverings of adjacent muscles is called an aponeurosis.
Step-by-step explanation:
The broad sheet of dense connective tissue that attaches the coverings of adjacent muscles is called an aponeurosis. In skeletal muscles, the connective tissue layers (mysia) intertwine with tendons, and in the lower back, the aponeurosis is an example of this fusion.