Variation archive

854 published articles

• Encyclopedia entry9 August 2026

  Clavicle

  The clavicle is often (2-6% of cases) traversed by a small canal which provides passage for one of the intermediate supraclavicular nerves. Santos reported the frequency to be about 6.6%. This canal reportedly occurs more frequently on the left side. The costoclavicular ligament may cause a deep impression in the clavicle, which may be mistakenly identified as a lesion when seen in x-ray films. The coracoclavicular syndesmosis may be a diarthrosis or a cartilaginous symphysis.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Wrist and Hand: Carpals, Metacarpals and Phalanges

  The numbers of carpal bones are frequently and variably increased. Over 20 accessory ossicles have been described. These usually occur because of failure of fusion of ossification centers. Such is the case of the os centrale, an additional bone located on the dorsal aspect between the scaphoid, capitate, and trapezoid, or between the lunate, triquetrum, and hamate. It is formed when a small cartilagenous nodule fails to fuse with the scaphoid, and may be doubled. Additional elements appear in connection with the trapezium and hamate.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Cervical Vertebrae

  The cervical vertebrae exhibit considerable variation in their spinous processes. As a rule, in the White race, the second, third, fourth, and fifth vertebrae possess bifid spines. The sixth and seventh demonstrate a tendency to be bifid with two small lateral tubercles. The sixth occasionally has a bifid spine, the seventh rarely. Occasionally all the cervical spines, with the exception of the second, are nonbifid. In the "colored races", the cervical spines are relatively shorter than in whites generally and, as a rule , are simple.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Arm: Humerus

  The humeral head may be absent. The humerus may have an enlarged deltoid process. The olecranon fossa of the humerus is occasionally perforated to form a supratrochlear foramen or septal aperature. Septal aperatures may occur in 4-13% of individuals, more frequently on the left side and in females. Racial variations of 4.1-58% have been reported. In an examination of 1744 arm bones, Trotter found septal apertures in 4.2% of whites and 12.8% of American Negroes.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Ankle and Foot: Tarsals, Metatarsals and Phalanges

  The tarsal bones are variable in size, form, and number. About 30 accessory tarsal ossicles have been described. The diversity has been related partially to their function in weight bearing. The tarsal bones are commonly reduced to six through the fusion of the calcaneous and the navicular. Additional elements to the normal seven may occur in the tarsus. The most frequent is the presence of a triangular bone (os trigonum), which may result from lack of fusion between the lateral tubercle of the posterior process of the talus and the primary ossification center of the bone.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Vestibulocochlear

  See: Facial Nerve

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Vagus (CN X) Nerve

  The right and left vagus may differ significantly in size. The nerves may lie in front of both vessels (internal carotid and internal jugular) in the carotid sheath. The left vagus has been found passing anterior to the common carotid artery and the thyroid gland. Descendens hypoglossi (C1 and C2) may be carried partly or completely by the vagus nerve instead of the hypoglossal nerve. The distribution of the right and left vagus nerves around the esophageal hiatus is variable. The vagus nerve may contain accessory parathyroid tissue. See also Recurrent Laryngeal Nerve.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Trochlear (CN IV) Nerve

  Variations in the branches and orbital course of the trochlear nerve have been described. The nerve has been reported to send a branch to M. orbicularis palpebrarum (orbicularis oculi) and to join sensory nerves (frontal, suprtrochlear, infratrochlear, and nasal). These branches probably represent an aberrant course of sensory fibers from the trigeminal nerve. One variation in the orbital course consists of the trochlear piercing (instead of coursing over) M. levator palpebrae superioris on its way to the superior oblique muscle.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Zygomatic Nerve

  The following variations have been reported in this nerve or its two branches (the temporal or facial or malar). The nerve may pass through the zygomatic bone before it divides into two branches, or the two branches may pass separately through foramina in the zygomatic bone instead of passing through a common foramen (sphenozygomatic foramen). The temporal branch in some cases passes through the sphenomaxillary fissure into the temporal fossa.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Trigeminal (CN V) Nerve — Ophthalmic Division (V1)

  Ophthalmic Division (V1)

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Twelfth Thoracic Nerve

  In 50% of cases studied, the twelfth thoracic participates in the lumbosacral plexus.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Thoracic Spinal Nerves

  Defects in roots of thoracic nerves have been reported. In one study of 16 spinal cords, only three had the full complement of thoracic roots. In three cases, one thoracic spinal nerve (dorsal and ventral roots) was absent; in three, a dorsal root was absent; and in seven, a ventral root was absent. The first thoracic may fail to contribute to the formation of the posterior cord of the brachial plexus or it may be the sole source of the medial cord of the plexus. The first and second thoracic nerves are occasionally joined by a connecting branch.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Third and Fourth Sacral Nerves

  The levator ani may be supplied by either the third or the fourth sacral nerves. In one study of 30 subjects, the levator muscle was supplied by the third sacral in 17 and by the fourth sacral in 13 subjects References Cruveilhier, J Traité d'Anatomie Descriptive, 3rd ed., G. Doin & Cie., Paris. Henle, J. (1868) Handbuch der Systematischen Anatomie des Menschen. von Friedrich Veweg und Sohn, Baunschweig. Jackson, C.M., Ed. (1933) Morris' Human Anatomy, 9th ed., P. Blakiston's Son & Co., Inc., Philadelphia. Kopsch, F. (1908) Rauber's Lehrbuch der Anatomie des Menschen. Georg Thieme, Leipzig.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Temporal Branch of Facial Nerve

  See also: Facial Nerve

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Sympathetic Nerves Presacral

  See also: Sacral Ganglia

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Sympathetic Nerves Heart

  See also: Cardiac Plexus

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Sural Nerve

  See also: Tibial and Sural Nerves

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Supreme Splanchnic Nerve

  Wrisberg observed a supreme splanchnic nerve eight times in a "large number" of bodies. It was described as being formed by branches from cardiac nerves, and from lower cervical and upper thoracic ganglia.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Superior Laryngeal Nerve

  Instead of its usual course on the medial side of the internal carotid artery, this nerve may pass lateral to the artery. The external laryngeal branch often arises independently from the main trunk. The superior laryngeal nerve may anastomose with the recurrent laryngeal nerve.

  • Not assessed by the portal — what this means
• Encyclopedia entry9 August 2026

  Superior Cervical Ganglion

  The superior cervical ganglion may be doubled, with one part superficial to and the other posterior to the carotid sheath. A variable number of fibers from the superior ganglion join the inferior ganglion of the vagus, hypoglossal, and descendens cervicalis nerves. Ganglion cells, intermingled with nerve fibers from the sympathetic trunk, have been reported within the cranium.

  • Not assessed by the portal — what this means