​Muscle groups are separated by membranes called:

A) ​sheaths
B) ​tissue
C) ​extensors
D) ​sphincters

Sheaths

Protective coverings or cases that enclose a part or object, such as a blade or a cable.

Extensors

muscles that increase the angle between components of a limb, working to extend or straighten out the limb.

Tissue

Groups of similar cells in an organism that work together to perform specific functions.