854 published articles
The radial nerve may accompany the axillary (circumflex) nerve through the quadrangular space (bounded by mm subscapularis and teres minor above, teres major below, the humeral head of the triceps medially, and the humerus laterally). The radial nerve may communicate with the ulnar nerve in the arm.
The posterior interosseous nerve may pass over instead of perforating the supinator muscle. It may supply the anconeus muscle, extensor carpi radialis brevis (36% of cases), and the opposed surfaces of the middle and index fingers. The posterior and anterior interosseous nerves sometimes communicate.
The medial pectoral (from the medial cord of the brachial plexus) may supply twigs to the clavicular head of the deltoid muscle and the acromioclavicular articulation. The lateral pectoral (from the lateral cord of the brachial plexus) may not receive fibers from the first thoracic nerve. Cutaneous branches from the lateral pectoral nerve have been described supplying the skin of the mammary region and axilla. Fibers from the medial pectoral nerve that supply m. pectoralis major may wind around the lower border of pectoralis minor instead of piercing it.
The nerve to subclavius (C5) may supply a branch to the phrenic nerve (accessory phrenic nerve). It joins the phrenic nerve either at the root of the neck or less frequently in the thorax. Rarely, the entire phrenic nerve arises from this branch, in which case it crosses the third part of the subclavian artery. A branch may communicate with the lateral and medial pectoral nerves, and another may supply the clavicular head of the sternocleidomastoid muscle. Image 31A Image 31B Image 31C Image 31D Image 31E Image 31F Image 31G Image 31H Image 31I Image 31J
The following variations in the formation, course, and distribution of this nerve have been reported. The combination from the first thoracic nerve to the formation of the median nerve may be missing. Either the outer (lateral) or the inner (medial) branch (from the lateral and medial cords) of the nerve may consist of two nerve bundles. The site of union between the lateral and medial branches is quite variable and has been found as far down as the elbow. The two branches may enclose the axillary vein as well as the axillary artery.
This nerve arises from the lateral cord (90.5% of 75 arms), from the lateral and posterior (4%), from the median nerve (2%), as two separate bundles from the medial and lateral cords (1.4%), or from the posterior cord (1.4%). A number of variations in the course and distribution of the musculocutaneous nerve have been reported.
This nerve may receive fibers from the eighth cervical to the second thoracic nerves. The connection with the intercostobrachial nerve may be multiple (two or more communicating branches), forming a plexus at the posterior boundry of the axillary space. The nerve sometimes communicates with the lateral cutaneous branch of the third intercostal nerve. When absent, the medial brachial cutaneous is replaced (rarely) by a lateral cutaneous branch from the first thoracic nerve, which traverses the first intercostal space, or more commonly by the intercostobrachial nerve.
The posterior division of this nerve may (a) arise separately from the posterior branch of the lower trunk of the brachial plexus; (b) be joined with or replaced by a branch of the ulnar nerve; or (c) extend to the hand, replacing the dorsal branch of the ulnar nerve. Image 31A Image 31B Image 31C Image 31D Image 31E Image 31F Image 31G Image 31H Image 31I Image 31J Image 32A Image 32B Image 32C Image 32D Image 32E Image 32F
The following variations occur in the origin of this nerve. A contribution has been reported from the fourth cervical and from the fifth cervical nerve, which may not join the main trunk of the nerve but pass directly to the upper digitations of m. serratus anterior. The root from the seventh cervical nerve may be missing. An additional root from the eighth cervical nerve has been reported. Infrequently, the long thoracic nerve does not pass through scalenus medius and the nerve trunk is formed over the first rib. Hence, the upper part may pass throught the axilla unattached to the fascia.
This nerve usually arises from the radial, but it may also arise from the posterior brachial cutaneous nerve.
Instead of its usual location on the deep surface of the levator scapulae muscle, the nerve may pierce the muscle.
The brachial plexus is formed by the anterior primary divisions of the lower four cervical nerves and the greater part of the anterior primary division of the first thoracic nerve. It may be joined by branches from the fourth cervical and the second thoracic nerves. In one study of 175 plexuses, more than 60% received a communication from the fourth cervical nerve. Of those that did not receive a contribution from the fourth, almost 30% of the 175 plexuses studied received the entire anterior primary division of the fifth cervical.
The axillary nerve may be derived solely from the fifth cervical nerve; the contribution from the sixth cervical may be insignificant or absent altogether. It may pierce and supply a branch to m. subscapularis. Branches to the long head of the triceps and infraspinatus muscles have been described. The nerve to teres major may arise from the axillary nerve instead of the lower subscapular nerve. The axillary and lower subscapular nerves have been found traversing subscapularis beneath an accessory subscapular muscle. Breisch considered the arrangement a possible nerve entrapment site.
This nerve carries the otic ganglion, which is derived from glossopharyngeal neurons. The nerve usually arises by two roots from the posterior division of the mandibular nerve. The two roots usually surround the middle meningeal nerve before joining to form a single trunk. A variation in this relationship has been described in which the middle meningeal artery pierces the anterior root instead of passing between the two roots. According to Baumel, Vanderheiden and McElenney the auriculotemporal nerve is commonly misrepresented in both illustrations and textbooks.
This nerve may be absent, or may join with the main trunk of the facial nerve reaching its destination through the posterior auricular nerve. Communicating branches between the auricular and facial nerves or the auricular nerve that traverses the temporal bone, may be absent.
The anterior commissure may be absent. Reference Bruce, A. (1890) On the absence of the corpus callosum in the human brain with a description of a new case. Brain 12:171-190.
The ansa cervicalis may arise from the first, second and third or only from the second and third cervical nerves. The ramus descendens hypoglossi may be replaced by the vagus (CN X). When no ansa is present, the innervation of the infrahyoid muscles is by branches arising directly from C2 and C3. The nerve to the thyrohyoid may arise as a branch of the ramus descendens hypoglossi. The phrenic nerve may also receive a contribution from the descendens hypoglossi. Variable connections with the cervical sympathetic trunk have been reported.
Several variations have been reported in the course and/or distribution of this nerve. It may be absent on one side, in which case the extraocular muscle usually innervated by the abducens (the lateral rectus) is supplied by the oculomotor nerve. The abducens may leave the brain stem not as a single bundle but as several widely separated fascicles emerging from the lower border of the pons or between fibers of the pyramid. The abducens occasionally furnishes a branch to the superior rectus, or to the nasociliary nerve or even to the ciliary ganglion.
