Cross Sectional Anatomy -Back muscles

Using the diagram below, name the muscle labeled "A"

Iliocostalis - upper fibers

The classification of back muscles considered "true" muscles are:

Intrinsic

Which broad shaped triangle shaped muscle is considered the prime mover of arm extension, adduction, flexion and internal rotation of the shoulder? It is attached to the bicipital groove on the anterior surface of the humerus.

Latissimus dorsi

Which group of muscles are located medial to the iliocostalis group and has a thoracic and cervicis division? These muscles are responsible for extending the neck and bending the back backward

Longissimus

Which is NOT an intrinsic muscle?

Rhomboids

Using the diagram below, identify the indicated muscle

Serratus Posterior Superior

This intrinsic muscle is blended with the longissimus muscle. It is responsible for extending the vertebral column.

Spinalis thoracic

Using the diagram below, name the muscle labeled "B".

Spinalis thoracic

What makes the "true" muscles different in development that the other extrinsic back muscles?

They develop embryonically

An extrinsic triangle-shaped muscle innervated by CN XI and is responsible for elevating and retracting the scapula is:

Trapezius