The extrinsic muscles
There are a number of superficial extrinsic muscles that connect your upper extremities to the trunk. They form the V-shaped musculature associated with the middle and upper back. A colour coded image is shown below.
Colour Code Key
Triangle muscle extending over the back
(Light blue) Rhomboid Major
The muscle that connects your shoulder blade with your spine
(Green) Latissimus Dorsi
Large, flat muscle covering the mid to lower back
(Dark Blue) Rear Dealt
Muscle that makes up the posterior part of your shoulder
(Aqua) Teres Minor
Narrow muscle of the rotator cuff
(Orange) Teres Major
Muscle on the lower border of the shoulder blade
The Teres major muscle is a muscle of the upper limb.
This muscle attaches to the scapula and the humerus and is one of the seven scapulohumeral muscles. It is a thick but somewhat flattened muscle. The teres major muscle is positioned above the latissimus dorsi muscle and assists in the extension and medial rotation of the humerus. This muscle is commonly confused as a rotator cuff muscle, but it is not because it does not attach to the capsule of the shoulder joint, unlike the teres minor muscle for example.
Teres minor muscle
Narrow Elongated Muscle of the joint capsule.
The teres minor is a narrow, elongated muscle of the rotator cuff. The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the greater tubercle of the humerus and the posterior surface
Contrasting Teres Minor + Teres Major
Most of the muscles located in the upper and lower back are actually part of your core muscle group. The core muscle group is naturally the most important muscle group for strength training hence the reason they are called the “core” muscle group. If they weren’t the most important muscle group they would probably be called something like the “supporting” or “secondary” muscle group. Anyway, your back muscles are incredibly intertwined with many of the other muscles on your body. For example, the back muscles allow you to stand upright and move your arms and shoulders.