thin, transparent lamina of bone, which is sometimes perforated by a supratrochlear foramen; they are lined in the fresh state by the synovial membrane of the elbow-joint, and their margins afford attachment to the anterior and posterior ligaments of this articulation. the capitulum is a rounded eminence forming the lateral part of the distal humerus. the head of the radius articulates with the capitulum. capitulum on the lateral side and trochlea on the medial side of the humerus the trochlea is spool-shaped medial portion of the distal humerus and articulates with the ulna. trochlea of the humerus epicondyles the epicondyles are continuous above with the supracondylar ridges. the lateral epicondyle is a small, tuberculated eminence, curved a little forward, and giving attachment to the radial collateral ligament of the elbow-joint, and to a tendon common to the origin of the supinator and some of the extensor muscles. the medial epicondyle, larger and more prominent than the lateral, is directed a little backward; it gives attachment to the ulnar collateral ligament of the elbow-joint, to the pronator teres, and to a common tendon of origin of some of the flexor muscles of the forearm; the ulnar nerve runs in a groove on the back of this epicondyle. medial and lateral epicondyles of the humerus medial and lateral supracondylar ridges of the humerus the medial supracondylar crest forms the sharp medial border of the distal humerus continuing superiorly from the medial epicondyle. the lateral supracondylar crest forms the sharp lateral border of the distal humerus continuing superiorly from the lateral epicondyle. borders the medial portion of the articular surface is named the trochlea, and presents a deep depression between two well-marked borders; it is convex from before backward, concave from side to side, and occupies the anterior, lower, and posterior parts of the extremity. the lateral border separates it from the groove which articulates with the margin of the head of the radius. the medial border is thicker, of greater length, and consequently more prominent, than the lateral. the grooved portion of the articular surface fits accurately within the semilunar notch of the ulna; it is broader and deeper on the posterior than on the anterior aspect of the bone, and is inclined obliquely downward and forward toward the medial side. articulations at the shoulder, the head of the humerus articulates with the glenoid fossa of the scapula. more distally, at the elbow, the capitulum of the humerus articulates with the head of the radius, and the trochlea of the humerus articulates with the trochlear notch of the ulna. diagram of the human shoulder joint, front view diagram of the human shoulder joint, back view the left shoulder and acromioclavicular joints, and the proper ligaments of the scapula. head of humerus the supinator. nerves the axillary nerve is located at the proximal end, against the shoulder girdle. dislocation of the humerus's glenohumeral joint has the potential to injure the axillary nerve or the axillary artery. signs and symptoms of this dislocation include a loss of the normal shoulder contour and a palpable depression under the acromion. the radial nerve follows the humerus closely. at the midshaft of the humerus, the radial nerve travels from the posterior to the anterior aspect of the bone in the spiral groove. a fracture of the humerus in this region can result in radial nerve injury. the ulnar nerve lies at the distal end of the humerus near the elbow. when struck, it can cause a distinct tingling sensation, and sometimes a significant amount of pain. it is sometimes popularly referred to as 'the funny bone', possibly due to this sensation (a "funny" feeling), as well as the fact that the bone's name is a homophone of 'humorous'. it lies posterior to the medial epicondyle, and is easily damaged in elbow injuries. horizontal section at the middle of upper arm. horizontal section of upper arm. humerus function muscular attachment the deltoid originates on the lateral third of the clavicle, acromion and the crest of the spine of the scapula. it is inserted on the deltoid tuberosity of the humerus and has several actions including abduction, extension, and circumduction of the shoulder. the supraspinatus also originates on the spine of the scapula. it inserts on the greater tubercle of the humerus, and assists in abduction of the shoulder. the pectoralis major, teres major, and latissimus dorsi insert at the intertubercular groove of the humerus. they work to adduct and medially, or internally, rotate the humerus. the infraspinatus and teres minor insert on the greater tubercle, and work to laterally, or externally, rotate the humerus. in contrast, the subscapularis muscle inserts onto the lesser tubercle and works to medially, or internally, rotate the humerus. the biceps brachii, brachialis, and brachioradialis (which attaches distally) act to flex the elbow. (the biceps do not attach to the humerus.) the triceps brachii and anconeus extend the elbow, and attach to the posterior side of the humerus. the four muscles of supraspinatus, infraspinatus, teres minor and subscapularis form a musculo-ligamentous girdle called the rotator cuff. this cuff stabilizes the very mobile but inherently unstable glenohumeral joint. the other muscles are used as counterbalances for the actions of lifting/pulling and pressing/pushing. left humerus. anterior view. supraspinatus musclelatissimus dorsi musclepectoralis major muscledeltoid musclebrachioradialisextensor carpi radialis longus musclecommon extensor tendonsubscapularis muscleteres major musclecoracobrachialis musclebrachialis musclepronator teres musclecommon flexor tendon left humerus. posterior view. other animals primitive fossils of amphibians had little, if any, shaft connecting the upper and lower extremities, making their limbs very short. in most living tetrapods, however, the humerus has a similar form to that of humans. in many reptiles and some mammals (where it is the primitive state), the lower extremity includes a large opening called the entepicondylar foramen to allow the passage of nerves and blood vessels. additional images position of humerus (shown in red). animation. left humerus. animation. 3d image human arm bones diagram. humerus - inferior epiphysis. anterior view. trochlea. posterior view. humerus - inferior epiphysis. posterior view. humerus - superior epiphysis. anterior view. humerus - superior epiphysis. posterior view. elbow joint. deep dissection. anterior view. elbow joint. deep dissection. posterior view. elbow joint. deep dissection. posterior view. the left shoulder and acromioclavicular joints, and the proper ligaments of the scapula left humerus. anterior view. left humerus. posterior view. left humerus. anteriolateral view. left humerus. medial view. fracture of the proximal humerus left elbow-joint, showing anterior and ulnar collateral ligaments. capsule of elbow-joint (distended). posterior aspect. ossification further information: ossification during embryonic development, the humerus is one of the first structures to ossify, beginning with the first ossification center in the shaft of the bone. ossification of the humerus occurs predictably in the embryo and fetus, and is therefore used as a fetal biometric measurement when determining gestational age of a fetus. at birth, the neonatal humerus is only ossified in the shaft. the epiphyses are cartilaginous at birth. the medial humeral head develops an ossification center around 4 months of age and the greater tuberosity around 10 months of age. these ossification centers begin to fuse at 3 years of age. the process of ossification is complete by 13 years of age, though the epiphyseal plate (growth plate) persists until skeletal maturity, usually around 17 years of age.