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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.
See Deep Peroneal Nerve
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.
See Phrenic Nerve
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.
The vaginal or the vagino-vesical in females corresponds to the prostatic/vesical artery in males. This artery may arise from several sources, Dubreuil-Chambardel found the following: 1. Arises from the internal iliac in 40% of cases, 2. Arises from a common trunk with the middle rectal 19% 3. Arises from a common trunk with the uterine 16%, and 4. In the remainder, the artery is doubles 25%. From Dubreuil-Chambardel, 1925. Levi noted the duplication of the vaginal artery in 21 of 50 cases studied.
This artery arose from the umbilical in 99 of 132 cases reported. It was bilateral in 33 of 66 and unilateral in 33 of 66 bodies. When unilateral, it occurs with almost equal frequency from the right (18 of 33 cases) and left (15 of 33 )sides.
The inferior ulnar collateral may take the place of the superior ulnar collateral. It may be small, with the superior taking its place.
This artery may be supplemented by an accessory vessel.
Lizars, John. A system of anatomical plates of the human body. Lymphatics of the head and neck. Published in Edinburgh about 1840. The right lymphatic duct forms various combinations with the right subclavian vein and jugular trunks. It is rare to find a simple right lymphatic duct that enters directly into the junction of the internal jugular and subclavian veins. The thoracic duct, which drains most of the body, may end by joining the left internal jugular, the junction of the left internal jugular and left subclavian vein, or the brachiocephalic vein.