Book : Human Anatomy
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Posted by: CHELSEA
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Writer CHELSEA

Scapula

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In anatomy, the scapula is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones the scapulae are paired, with the scapula on the left side of the body being roughly a mirror image of the right scapula. In early Roman times, people thought the bone resembled a trowel, a small shovel. The shoulder blade is also called omo in Latin medical terminology. The scapula forms the back of the shoulder girdle. In humans, it is a flat bone, roughly triangular in shape, placed on a posterolateral aspect of the thoracic cage. 

The scapula is commonly referred to as the shoulder blade. It connects the humerus bone of the arm to the collarbone. There are only three muscles that are responsible for enabling the movement of the shoulder blade. The trapezius muscle implants into the collarbone. It is responsible for movement of the shoulder and head. The levator muscle is a small, thin muscle. It arises from the vertebrae of the neck. A small tendon attaches the levator to the upper area of the shoulder blade. This muscle is responsible for pulling up the scapula, which allows for the shrugging movement of the shoulders. The rhomboideus is actually two muscles, the major and minor, located deep in the base of the shoulder blade. These muscles are responsible for raising the shoulder blade and moving it backwards. The muscles that move the shoulder forward come from the breast. Upward movements are controlled by muscles located in the neck.

Like any triangle, the scapula consists of three borders: superior, lateral and medial. The superior border is the shortest and thinnest border of the three. The medial border is a thin border and runs parallel to the vertebral column and is therefore often called the vertebral border. The lateral border is often called the axillary border as it runs superolaterally towards the apex of the axilla and it is the thickest and strongest of the three borders for muscle attachment. It also has the glenoid cavity or socket along this border, a shallow fossa which articulates with the head of the humerus, forming the glenohumeral joint. There are also three angles to the scapula. The superior border meets the lateral border at the lateral angle and with the medial border at the superior angle. The third angle is the inferior angle where the medial and lateral borders meet.

The scapula has two surfaces; on the anterior aspect is the smooth costal surface which is concave in shape and is majorly taken up by the subscapular fossa. At the back of the scapula is the convex and uneven posterior surface which has a protruding ridge of bone (spine of the scapula) that unevenly separates it into two divisions: the superior supraspinous fossa and the much bigger, inferior infraspinous fossa.

Front Surface:

The front of the scapula (also known as the costal or ventral surface) has a broad concavity called the subscapular fossa, to which the subscapularis muscle attaches. The medial two-thirds of the fossa have 3 longitudinal oblique ridges and another thick ridge adjoins the lateral border, which run outward and upward. The ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the subscapularis muscle. The lateral third of the fossa is smooth and covered by the fibers of this muscle.
At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself along a line at right angles to and passing through the center of the glenoid cavity, forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion. The costal surface superior of the scapula is the origin of 1st digitation for the serratus anterior origin.
 
Back Surface:

The back of the scapula (also called the dorsal or posterior surface) is arched from above downward, and is subdivided into two unequal parts by the spine of the scapula. The portion above the spine is called the supraspinous fossa, and that below it the infraspinous fossa.

  • The supraspinous fossa, the smaller of the two, is concave, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds give origin to the Supraspinatus.
  • The infraspinous fossa is much larger than the preceding; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a prominent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part. The medial two-thirds of the fossa give origin to the Infraspinatus; the lateral third is covered by this muscle.
There is a ridge on the outer part of the back of the scapula. This runs from the lower part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm above the inferior angle. Attached to the ridge is a fibrous septum, which separates the infraspinatus muscle from the Teres major and Teres minor muscles. The upper two-thirds of the surface between the ridge and the axillary border is narrow, and is crossed near its center by a groove for the scapular circumflex vessels; the Teres minor attaches here.

The broad and narrow portions above alluded to are separated by an oblique line, which runs from the axillary border, downward and backward, to meet the elevated ridge: to it is attached a fibrous septum which separates the Teres muscles from each other.
Its lower third presents a broader, somewhat triangular surface, the Inferior angle of the scapula, which gives origin to the Teres major, and over which the Latissimus dorsi glides; frequently the latter muscle takes origin by a few fibers from this part.


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