Variation archive

754 published articles

• Encyclopedia entry9 August 2026

  Middle Cerebral Artery

  In a study of 25 brains (50 middle cerebral arteries), 10 forms of division were found. The principal forms of variation included: a) a single vessel arising proximal to the sylvian fissure (34%), b) more than one major vessel arising proximal to the sylvian fissure (26%), c) a trifurcation at the mouth of the sylvian fissure (34%), and d) a bifurcation at the mouth of the sylvian fissure (16%). The middle cerebral may be absent or replaced by a branch from the deep cerebral.

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• Encyclopedia entry9 August 2026

  Posterior Communicating Artery

  This artery may be absent or replaced by a branch from the middle cerebral. In one review of nine studies of 2362 brains, the posterior communicating artery was absent unilaterally in 3.09% and bilaterally in 0.3%. The posterior communicating artery is sometimes joined with the middle cerebral artery instead of the trunk of the internal carotid.

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• Encyclopedia entry9 August 2026

  Peroneal Artery

  The peroneal artey was found to be well-developed in 31 of 209 cadavers, about 15% of legs. It may arise (unusually) in the distal leg. It may also be absent or replaced by the posterior tibial. On occasion it gives rise to the anterior tibial, or rejoins the posterior tibial. An accessory peroneal artery has also been noted.

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• Encyclopedia entry9 August 2026

  Profunda Femoris Artery

  This artery may course lateral, medial or anterior to the femoral artery. If it arises from the medial aspect of the femoral, the femoral may appear to split into three vessels of almost equal caliber: femoral, profunda and lateral circumflex. Srb (1860) though that its position depended on whether it furnished the medial circumflex or not; the lateral circumflex tends to draw the profunda laterally. The profunda may pass medially superficial to the vein, and then continue in its usual way.

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• Encyclopedia entry9 August 2026

  Thoracoacromial Artery

  The thoracoacromial artery may be missing. In Poynter's series it was the second branch in 47% of individuals studied. In some cases the arteries that make up the trunk arise separately, and in other cases it may have four branches; supreme (superior) thoracic, thoracic branch of the thoracoacromial, accessory pectoral branches, and lateral thoracic. The thoracoacromial artery may send a branch to pectoralis minor (8%) This artery may have a common origin with some other artery in 24% of individuals.

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• Encyclopedia entry9 August 2026

  Obturator Artery

  This artery has received much attention due to its surgical interest connected with its origin from the epigastric artery. Poynter suggested that the first report of the origin of the obturator from the epigastric was that of Haller, 1745, note 9, who says ,"Non tamen perpetuum est cam arteriam a pelves truncis nasci, eam novies ex epigastrica ortam." Further that the surgical significance of the epigastric source seems to have been recognized by Monro in 1806.

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• Encyclopedia entry9 August 2026

  Middle Rectal Artery

  This artery may be absent. It may arise from the internal iliac with the inferior vesical artery. It has also been reported as arising with or from the internal pudendal, or inferior gluteal arteries. Unusual branches of the middle rectal include: the vaginal, seminal vesical, prostatic, and inferior lateral sacral arteries. In their report to the anatomical society of Great Britian and Ireland, Parsons and Keith, provided the following data. They had 45 observations.

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• Encyclopedia entry9 August 2026

  Middle Meningeal Artery

  The middle meningeal artery may be absent. In 99% of cases however, it enters the foramen spinosum. When this foramen is absent, the artery enters the foramen ovale , which is typically the foramen for the mandibular division of the trigeminal nerve. The middle meningeal gives rise, in about 50% of cases, to an accessory meningeal artery, which also enters the skull via the foramen ovale, or the emissary sphenoidal foramen (20% of cases). It may also supply a palatine branch.

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• Encyclopedia entry9 August 2026

  Middle Sacral Artery (Median Sacral)

  The middle sacral artery may deviated from the midline. It may arise in common with one or both of the fifth pair of lumbar arteries, or from the bifurcation of the aorta, or from one of the iliac arteries, more frequently from the left. It often provides, from each side, a large branch (the lowest lumbar artery), which courses backwards onto the fifth lumbar vertebra (see illustration from Tiedemann). The middle sacral artery may also provide an "accessory" renal or, a middle rectal artery. The middle sacral artery may also provide a renal artery in cases of pelvic kidney.

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• Encyclopedia entry9 August 2026

  Lumbar Arteries

  One or more pairs of the lumbar arteries may arise as a common stem from the back of the aorta. The first lumbar may be joined at its origin with the lowest intercostal artery; the third and fourth lumbar, or less often the second and third lumbars, may arise from the aorta as a common stem. The fifth pair is sometimes absent. One or both of the last pair of lumbar arteries may arise in common with the middle sacral.

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• Encyclopedia entry9 August 2026

  Lateral Thoracic Artery

  This artery may arise from the thoracoacromial (12% of individuals, Poynter). The lateral thoracic may be replaced by or it may replace the thoracodorsal. On rare occasions it gives rise to the ulnar artery, and itself may be a branch of the subscapular (8%, Poynter). In about 24% of individuals the lateral thoracic is doubled. Poynter found the distribution to the intercostal spaces to be irregular; the second space received no supply in 15% and the axillary sent another branch to supply this intercostal space in 17%.

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• Encyclopedia entry9 August 2026

  Medial and Lateral Femoral Circumflex Arteries

  Variations of the medial femoral circumflex artery include the following. It may arise from the profunda femoris before the lateral circumflex; from the femoral artery, external iliac (2%) or one of its branches, or superficial epigastric; or from the the inferior epigastric artery or it may be the source of the inferior epigastric. The artery of ligamentum teres femoris arises from the medial femoral circumflex in about 15% of cases, from the obturator and medial circumflex via an anastomotic connection in about 24%, and from both arteries independently in about 7%.

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• Encyclopedia entry9 August 2026

  Ulnar Artery

  The ulnar artery may arise from the brachial above the usual point of division or from the axillary, in which case it usually passes over the flexor muscles, but beneath the fascia, to reach its usual position in the forearm. In circumstances such as this, the artery may terminate in the proximal forearm with a persistent median artery supplying the superficial arch The recurrent arteries and the common interosseous are usually derived from the trunk vessel from which the ulnar arises.

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• Encyclopedia entry9 August 2026

  Lateral Internal Thoracic Artery

  The internal thoracic may give rise to a lateral internal thoracic as it enters the thorax. The lateral internal thoracic runs about midway between the spine and the sternum or somewhat forward, spans up to six intercostal spaces, and anastomoses with the intercostal arteries of those spaces. A lateral internal thoracic artery may arise from the costocervical trunk, thyrocervical trunk, or ascending cervical. The possible existence of this vessel must be remembered when paracentesis is performed.

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• Encyclopedia entry9 August 2026

  Variations in the Branches of the Subclavian Artery

  There is considerable variation in the branching of the subclavian artery, and the branches may be arranged differently on the two sides of the body. The usual branching order on the right side is for the vertebral, thyrocervical trunk (common trunk for the inferior thyroid, transverse cervical, and suprascapular arteries, in 50% of cases), and the internal thoracic (internal mammary) to arise from the first part of the right subclavian.

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• Encyclopedia entry9 August 2026

  Internal Thoracic Artery

  The origins of this artery may vary as follows: a) It may arise from the subclavian, behind or in front of scalenus anterior; b) the right artery may arise from the ascending aorta; or c) it may arise in common with the inferior thyroid. The left internal thoracic artery has been shown by Robicsek, et al.(1967), to give rise to a anterior interventricular (descending) coronary artery, the usual supply being the left anterior descending coronary artery (LAD-CA).

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• Encyclopedia entry9 August 2026

  Suprascapular Artery

  In a study of 400 cadavers, the suprascapular artery arose from the thyrocervical trunk in about 92%, internal thoracic in 4.1%, and transverse cervical in 2.5%, independently from the subclavian in about 2%, and rarely from the axillary, costocervical trunk, or from the dorsal scapular artery. It may arise from the subclavian or axillary artery (reported as high as 10%), or from an accessory inferior thyroid, the subscapular, or the thoracoacromial artery. When it arises from the second or third part of the subclavian, it usually passes through, rather than over the brachial plexus.

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• Encyclopedia entry9 August 2026

  Inferior Thyroid Artery

  In a study of 200 cadavers, the inferior thyroid arose from the thyrocervical trunk in 90.5%, subclavian in 7.5%, and very rarely from the common carotid, aortic arch, brachiocephalic, internal thoracic, pericardiacophrenic, or vertebral, or arose as a common stem with the contralateral inferior thyroid. The inferior thyroid may also arise as a common trunk with the dorsal scapular and suprascapular arteries (thyroscapular trunk). It may course behind the common carotid.

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• Encyclopedia entry9 August 2026

  Umbilical Artery

  This artery may provide a vesicodeferential, middle rectal, vaginal, accessory inferior epigastric, or an inguinal branch. An umbilical artery may be absent.

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• Encyclopedia entry9 August 2026

  Inferior and Superior Epigastric Arteries

  The inferior epigastric artery was not well understood until Mall (1898; F.P. Mall, an Iowan by birth, Belle Plaine, medically trained in Germany was the first Professor of Anatomy at The Johns Hopkins Medical School) studied its development. This artery has received much attention in the literature because of its relation to femoral hernia. It was shown in 1813 by Beckers that when the artery originated beneath the inguinal ligament it passed medial to the inguinal ring.

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