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It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a rounded head, a narrow neck, and two short processes (tubercles, sometimes called tuberosities). The body is cylindrical in its upper portion, and more prismatic below.
It gives attachment to the capsular ligament of the shoulder joint except at the upper inferior-medial aspects. It is best marked in the lower half of its circumference; in the upper half it is represented by a narrow groove separating the head of the humerus from the two tubercles, the greater tubercle and the lesser tubercle.
Bones are commonly described with the terms head, neck, shaft, body and base. The head of a bone usually refers to the distal end of the bone. The shaft refers to the elongated sections of long bone, and the neck the segment between the head and shaft (or body). The end of the long bone opposite to the head is known as the base.
The ligaments may be best seen by opening the capsule at the back of the joint and removing the head of the humerus: [2]. One on the medial side of the joint passes from the medial edge of the glenoid cavity to the lower part of the lesser tubercle of the humerus.
The lesser tubercle of the humerus, although smaller, is more prominent than the greater tubercle: it is situated in front, and is directed medially and anteriorly.. The projection of the lesser tubercle is anterior from the junction that is found between the anatomical neck and the shaft of the humerus and easily identified due to the intertubercular sulcus (Bicipital groove).
The greater tubercle of the humerus is the outward part the upper end of that bone, adjacent to the large rounded prominence of the humerus head. It provides attachment points for the supraspinatus, infraspinatus, and teres minor muscles, three of the four muscles of the rotator cuff, a muscle group that stabilizes the shoulder joint.
The lateral intermuscular septum extends from the lower part of the crest of the greater tubercle of the humerus, along the lateral supracondylar ridge, to the lateral epicondyle; it is blended with the tendon of the deltoid muscle, gives attachment to the triceps brachii behind, and to the brachialis, brachioradialis, and extensor carpi radialis longus muscles in front.
The size and orientation of its functionally important features, including the deltoid tubercle, greater tubercle, and medial epicondyle, are pivotal to an animal's style of locomotion and habitat. In cursorial (running) animals such as the pronghorn , the deltoid tubercle is located about a quarter of the way down the shaft, which allows for ...