The infraspinatus
muscle is attached along the
broad inner
edge of the scapula (
shoulder blade). It narrows into a
strong tendonthat joins firmly to the top of the
humerus (upper arm
bone). The
infraspinatus muscle sits on the back of the shoulder blade
below the
spine and under the
deltoid muscle. It works with the
supraspinatus to help
lift and
twist the
upper arm. These
two muscles also help
support and
protect the
shoulder joint by keeping the head of the
humerus in place.
The base of this triangular muscle is attached along the lumbar and lower half of the thoracic vertebrae (spine), the lower ribs, and even the hip bones far below. The latissimus dorsi is a wide, flat muscle located on the lower half of the back. The muscle fibers at its tip insert under the scapula (shoulder blade) and join to the humerus (upper arm bone) in the shoulder. This muscle gives your arms motion. It is used when swimming or when you swing your arms back when jogging. It is also used to reach up to grab something above your head.
From: http://www.american.edu/adonahue/m5back.htm