Acromion

Bone: Acromion
Plan of ossification of the scapula. Posterior side. From seven centers. (Acromion visible at upper left, in blue.)
Left scapula. Lateral view. (Acromion labeled at upper right.)
Gray's	subject #50 203

The acromion process, or simply the acromion (from Greek: akros, "highest", ōmos, "shoulder"), is an anatomical feature on the shoulder blade (scapula), together with the coracoid process extending laterally over the shoulder joint.

In humans

It is a continuation of the scapular spine, and hooks over anteriorly.

The acromion articulates with the clavicle to form the acromioclavicular joint.

The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the glenoid cavity.

Surfaces

• Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibers of the Deltoideus, and in the rest of its extent is subcutaneous.
• Its inferior surface is smooth and concave.

Borders

• Its lateral border is thick and irregular, and presents three or four tubercles for the tendinous origins of the Deltoideus.
• Its medial border, shorter than the lateral, is concave, gives attachment to a portion of the trapezius, and presents about its center a small oval surface for articulation with the acromial end of the clavicle.

Os acromiale

In childhood the acromion has a separate center of ossification and is joined to the rest of the scapula by cartilage. Rarely, the acromion stays in adulthood as a separate bone called "os acromiale". This feature was common in skeletons recovered from the Mary Rose shipwreck: it is thought that in those men, much archery practice from childhood on with the mediaeval war bow (which needs a pull 3 times as strong as the modern standard Olympic bow) pulled at the acromion so much that it prevented bony fusion of the acromion with the scapula.

In animals

The acromion process of bats (Mammalia: Chiroptera) is particularly elongated compared to that of humans. Turtles (Reptilia: Testudinata) have an acromion that forms the anteriormost of the three "branches" of their triradiate pectoral girdle (together with coracoid bone and scapula).

Additional images

• 

  Diagram of the human shoulder joint

• 

  The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula.

• 

  Muscles connecting the upper extremity to the vertebral column.

• 

  Human arm bones diagram

External links

• acromion at eMedicine Dictionary
• Bioweb at UWLAX aplab
• Anatomy at Dartmouth Upperextremity/shoulder/bone-quiz/Q1

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.