Infraspinous fossa

The infraspinous fossa is the shallow, broad depression on the back of the scapula below the spine. In Anatomy and Physiology I, it is identified as the attachment site for the infraspinatus muscle.

What is the infraspinous fossa?

The infraspinous fossa is the large, slightly concave surface on the posterior scapula below the spine of the scapula. In Anatomy and Physiology I, you usually meet it when you are identifying bony landmarks on the shoulder blade and matching them to muscle attachments.

Think of the scapula as a flat, triangular bone with surfaces and ridges that organize the muscles around the shoulder. The spine of the scapula runs across the back of the bone like a raised ridge, and the infraspinous fossa sits underneath it. The term itself gives you a clue: infra means below, so the fossa is the depression below the spine.

This area is not a deep hole. It is more of a broad, gently hollowed surface that gives the infraspinatus muscle a place to attach. Because the scapula is a moving bone that glides over the rib cage, its surfaces are built for muscle attachment rather than weight bearing. That makes the infraspinous fossa part of the shoulder's motion system, not just a label to memorize.

The infraspinatus muscle fills this region and helps stabilize the shoulder joint. When you rotate your arm outward, the muscle acts on the humerus at the glenohumeral joint. The fossa itself does not create movement, but it anchors the muscle that does.

In lab, you would identify the infraspinous fossa on a scapula model or bone image by first finding the spine of the scapula, then locating the larger depression below it. If you can spot that ridge, the fossa is usually the next feature to name.

Why the infraspinous fossa matters in Anatomy and Physiology I

The infraspinous fossa matters because it links a bone landmark to a functional muscle attachment. In Anatomy and Physiology I, that connection is the whole point of skeletal anatomy: you are not just naming parts, you are tracing how structure supports movement.

This fossa also helps you orient the scapula quickly. Once you find the spine, you can tell the posterior surface from the anterior surface and avoid mixing up the glenoid side, acromion, and the muscle attachment areas. That kind of orientation comes up a lot in bone ID quizzes and lab practicals.

It also ties into shoulder mechanics. The infraspinous fossa anchors the infraspinatus, one of the rotator cuff muscles. If you know where the muscle begins, it is easier to understand how it helps stabilize the humeral head during arm movement and keeps the shoulder from slipping during rotation.

So this term is a small landmark with a big payoff: it helps you read the scapula as a working surface for muscle attachment, not just as a shape to memorize.

How the infraspinous fossa connects across the course

Scapula

The infraspinous fossa is one feature on the scapula, so you need the whole bone's layout to place it correctly. If you know the scapula's spine, body, and borders, the fossa becomes easier to find on a model or image. It is part of how the posterior scapula organizes shoulder muscles.

Spine of Scapula

The spine of the scapula is the ridge that separates the supraspinous and infraspinous fossae. That ridge is the landmark you use first when identifying the fossa below it. In lab, if you misidentify the spine, the rest of the posterior scapular anatomy can get mixed up fast.

Infraspinatus Muscle

The infraspinous fossa is the main origin area for the infraspinatus muscle. That makes the fossa a structural attachment site rather than an active mover itself. Once you connect the fossa to the muscle, it is easier to remember why the region belongs to the shoulder's stabilization system.

Acromion Process

The acromion process is another landmark on the scapula, but it sits more laterally and superiorly than the infraspinous fossa. Students often learn both together because they are part of the same bone and help map the posterior shoulder. Knowing where each one sits makes bone ID much faster.

Is the infraspinous fossa on the Anatomy and Physiology I exam?

A bone-identification question may show you a posterior scapula and ask you to label the depression below the spine. A lab practical can also ask which muscle attaches there, which points you to the infraspinatus. In a movement question, you may need to connect the landmark to shoulder external rotation and stabilization. The easiest strategy is to find the spine of the scapula first, then name the larger area below it. If a question includes the rotator cuff, this landmark helps you link structure to function instead of guessing from memory.

Key things to remember about the infraspinous fossa

• The infraspinous fossa is the broad depression on the posterior scapula below the spine of the scapula.

• Its main job in anatomy terms is to provide an attachment site for the infraspinatus muscle.

• You identify it by finding the spine of the scapula first, then looking at the surface below that ridge.

• This landmark matters because it connects a bone feature to shoulder movement and stability.

• In lab, it is a common bone-ID feature on scapula models, diagrams, and practicals.

Frequently asked questions about the infraspinous fossa

What is the infraspinous fossa in Anatomy and Physiology I?

It is the shallow depression on the back of the scapula below the spine of the scapula. In A&P I, you learn it as a bony landmark where the infraspinatus muscle attaches. The name is a clue, since infra means below.

Where is the infraspinous fossa located?

It is on the posterior surface of the scapula, underneath the spine of the scapula. If you are looking at a scapula model, find the spine first and then look at the larger area below it. That lower region is the infraspinous fossa.

What muscle attaches to the infraspinous fossa?

The infraspinatus muscle attaches there. That connection matters because the muscle is part of the rotator cuff and helps with external rotation and shoulder stability. The fossa itself is the attachment site, not the muscle.

How is the infraspinous fossa different from the supraspinous fossa?

The infraspinous fossa is below the spine of the scapula, while the supraspinous fossa is above it. They are easy to confuse because both are shallow depressions on the posterior scapula. The spine is the landmark that separates them.