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This nerve may be limited to the nasal cavity. It may also traverse the posterior ethmoidal foramen to gain entrance into the cranial cavity.
See also: Facial (CN VII) Nerve
The following variations in the digital distribution of this nerve has been reported. The nerve may have no digital branches whatsoever. It may supply the medial side of the great toe, adjacent sides of the second and third toes, or the lateral three and one-half toes. Absence of the cutaneous part of the superficial peroneal and the deep peronal nerve and its branch to extensor digitorum brevis has been reported. In this case the nerves were replaced by the saphenous and sural nerves.
See also: Brachial Plexus Cervical Plexus Lumbosacral Plexus Image 63A Image 63B Image 63C Image 63D Image 63E Image 63F Image 63G Image 63H Image 63I Image 63J
The sciatic usually divides into the common peroneal and tibial nerves at the level of the lower thigh. Very often these two nerves arise separately from the sacral plexus. They may be separated in the greater sciatic foramen by the piriformis muscle and pass into the thigh as contiguous but separate structures. Huelke (1958) reported that the peroneal communicating nerve arose directly from the common peroneal nerve in 54.7%, usually as a branch separate from the lateral sural cutaneous nerve (41.5%).
Although usually regarded as a subdivision of the pudendal plexus, this plexus has been described with the coccygeal nerves. It is usually formed by the anterior division of the fifth sacral and coccygeal nerves; it may receive contributions from the fourth sacral as well.
This ganglion contains preganglionic nerves and postganglionic neurons of the oculomotor nerve. The following variations in the size and roots of this ganglion has been reported. It may be absent or very small (grossly identifiable), in which case its constituent neurons are scattered among the nerve fibers associated with the ganglion (oculomotor and the ophthalmic division of the trigeminal). The ganglion may be doubled or even tripled. The motor root (branch of the oculomotor nerve to the inferior oblique muscle) sometimes bifurcates before reaching the ganglion.
When the ansa cervicalis is absent, the third cervical participates in the innervation of the infrahyoid muscles.
See also: Cervical Plexus Image 31A Image 31B Image 31C Image 31D Image 31E Image 31F Image 31G Image 31H Image 31I Image 31J
The greater occipital branch of the second cervical nerve has been reported to send a branch to the auricle. The greater and lesser occipital nerves complement each other, with each one compensating for any deficiency in the nerve supply of each other. The external (lateral) branch of the second cervical nerve may have a cutaneous branch in addition to its usual muscular branches; it may also supply the suboccipital superior oblique muscle in addition to its usual supply to the semispinalis cervicis, inferior oblique, semispinalis cervicic, and multifidus spinae muscles.
The dorsal root of the first cervical nerve is sometimes absent (8%). The root may arise partly or wholly from, or in common with, the accessory nerve. The dorsal branch of the first cervical nerve (the suboccipital nerve) occasionally supplies a cutaneous branch to the back of the head. It accompanies the occipital artery and is joined beneath the skin with the greater and lesser occipital nerves. (See also Vagus (CN X) and Hypoglossal (CN XII) Nerves).
The cutaneous branches of the fifth and sixth cervical nerves may be very small or completely absent. The upper subscapular nerve arises from the fifth and sixth, but in 50% of cases it also receives a contribution from the fourth. Image 31A Image 31B Image 31C Image 31D Image 31E Image 31F Image 31G Image 31H Image 31I Image 31J
The eight cervical nerve may give rise to a cutaneous branch of considerable size. Reference Schaefer, E.A., Symington, J. and T.H. Bryce., Eds., (1915) Quain's Anatomy, 11th ed., Longmans, Green, and Co., London.
Communicating branches between the cervical sympathetic trunk and descendens cervicalis are variable. In one study, the following patterns were noted: communicating branches were found (a) between the superior cervical ganglion and descendens cervicalis; (b) joining C2 and C3; and (c) variably joining the connecting loop between C2 and C3.
Instead of a single nerve, the superficial cervical may have two or more branches arising from the cervical plexus The nerve may arise solely from the third or from the third and fourth cervical nerves. In its course in the neck it sometimes passes through an annulus in the external jugular.
The following variations in origin, course, and distribution of the phrenic nerve have been reported. The phrenic nerve may receive additional roots from one or more of the following nerves: nerve to subclavius; nerve to sternohyoid; second or rarely, sixth cervical nerve; descendens cervicalis; ansa cervicalis; and brachial plexus. It may receive a branch from CN XII (hypoglossal) and may communicate with CN XI (spinal accessory). The phrenic nerve may arise exclusively from the nerve to subclavius. On occasion it supplies a branch to the subclavius muscle.
The lesser occipital nerve may be very small and distributed only to the skin of the neck. In such cases, the greater occipital nerve supplies the areas usually supplied by the lesser occipital. In some cases instead of its usual dorsal and upward course beneath the deep fascia along the posterior border of the sternocleidomastoid muscle, the lesser occipital nerve passes directly backward, piercing the trapezius muscle near its upper border before reaching the scalp. The auricular branch of the lesser occipital nerve may be derived from the greater occipital.
The mastoid branch of the great auricular nerve may arise independently from the cervical plexus, in which case it passes upward between the lesser occipital and great auricular nerves to reach its destination. The great auricular nerve may arise solely from the third or from the third and fourth cervical nerves.
An additional communicating branch from the fourth cervical nerve may join the descending cervical nerve in the ansa cervicalis.
The cervical plexus consists of three loops. A large part of the anterior primary division of the first cervical nerve is given to the hypoglossal or cervical loop. The remainder contributes to the cervical plexus thus forming the first loop. From the first loop of the plexus, two branches of the first cervical nerve usually enter the sheath of the hypoglossal nerve (or may instead enter the sheath of the vagus nerve) and descend with it to contribute to the hypoglossal or cervical loop.