The two shoulder girdles are each composed of two bones, the scapula and the clavicle. The scapula is a triangular bone with a lateral socket, the glenoid cavity, for the humerus of the arm. There are two processes which project above the level of the glenoid cavity. The superior of these processes is the acromion (acros = Gr. topmost, height). The acromion is an extension of the posterior spine and articulates with the clavicle.
The second process, the coracoid process, lies superior and anterior to the glenoid cavity. The coracoid process is a site of muscle attachment.
The clavicle, or collarbone, is an S-shaped bone which articulates with the acromion of the scapula and the manubrium of the sternum. The sternal extremity is more rounded in shape than the acromial extremity. A roughened conoid tubercle is located on the inferior, posterior surface of the clavicle.
Figure 11.1 Shoulder Girdle and Arm
Figure 11.1 Shoulder Girdle and Arm
Acromial extremity Acromion Capitulum Carpus Clavicle Conoid tubercle Coracoid process Coronoid fossa Coronoid process Deltoid tuberosity Distal phalanx Glenoid cavity (X2) Head of humerus Head of radius Head of ulna Lateral epicondyle Medial epicondyle Metacarpal 1 Metacarpal 5 Middle phalanx Olecranon process Olecranon fossa Phalanges Proximal phalanx Radial notch Spine Sternal extremity Styloid process of radius Styloid process of ulna Trochlea
The upper arm bone is the humerus. (Please note the spelling of this word, it does not contain an "o"!) The head of the humerus is a spherical projection which articulates with the glenoid cavity of the scapula. Approximately halfway down the anterior surface of the humerus is the deltoid tuberosity, the site of attachment of the deltoid muscle.
There are a number of bone markings on the distal end of the humerus. The most prominent of these is the large olecranon fossa on the posterior surface of the distal end. On the anterior surface are the medial trochlea and the lateral capitulum. It will help you to realize that the trochlea has two "bumps" and is on the same side as the head. Just proximal to the trochlea is the coronoid fossa. The capitulum has only one rounded "bump". The final two processes on the distal end of the humerus are the lateral epicondyle and the medial epicondyle.
The distal bones of the arm are the lateral radius and the medial ulna. Examine the ulna first.
The proximal end of the ulna has a prominent fossa called the trochlear notch. With what structure does this process articulate?_ The coronoid process forms the anterior border of the trochlear notch. Posterior to the trochlear notch is the elbow, known to anatomists as the olecranon process. Put the ulna together with the humerus and notice how the olecranon fits into the olecranon fossa and the coronoid process into the coronoid fossa as the ulna hinges around the trochlea. There is a small radial notch on the lateral surface of the ulna distal to the trochlear notch. The radius articulates here.
The distal end of the ulna is the head. The ulna is the only bone in the body that "stands on its head". The short, medial projection off the head is the styloid process of the ulna.
The radius has fewer markings than the ulna. The proximal end of the radius is the head which articulates with the radial notch of the ulna and the capitulum of the humerus. Examine the articulated skeleton to see how the radius rotates around the capitulum. Distal to the head is the radial tuberosity, the site of muscle attachments. On the distal end of the radius is the styloid process of the radius. Note how the two styloid processes (one on the ulna and the other on the radius) are arranged to hold the bones of the wrist in place.
There are eight bones of the wrist called carpals. Collectively they are known as the carpus. They are arranged in two "rows". Examine the anterior surface of the wrist. The carpals of the distal row, from lateral to medial, are the trapezium, trapezoid, capitate, and hamate. Returning to the lateral side, the bones of the proximal row are the pisiform, triquetrum (triquetral), lunate, and scaphoid. You will not be asked to identify the bones of the carpus apart from each other, but you should be able to identify them in an articulated wrist. A mnemonic device which may help you is the phrase "Tiny Tim Could Hardly Pull The Little Sled". Each word begins with the same letter as a carpal beginning with the anterior, distal row, lateral to medial, and then back through the proximal row, medial to lateral. You should be able to name the bones from both the anterior and posterior views.
Distal to the carpals are the five metacarpals. These five bones are numbered from lateral to medial, i.e. metacarpal I articulates with the thumb. Note that the metacarpals are the bones of the palm.
Distal to the metacarpals are the fourteen phalanges (sing. - phalanx). Each finger has three phalanges named proximal phalanx, middle phalanx, and distal phalanx. The thumb has only two phalanges, the proximal and distal.
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