These fan-shaped or feather-shaped muscles have densely packed fibres, making them strong. There are different kinds of pinnate muscle, each adapted for specific work.
Unipennate muscle
The fibres of these muscles fan out from the narrow point at which they insert into the tendon. This makes the muscle strong. Some hand muscles are unipennate.
Bipennate muscle
This has fibres running diagonally from each side of a tendon, like a feather. This makes the muscle even stronger, but less mobile. The rectus femoris muscle at the front of the thigh is bipennate.
Multipennate muscle
This powerful muscle has many rows of fibres running from a central tendon. The deltoid (shoulder) muscle is multipennate.
Picture Credit : Google