Variation archive

854 published articles

• Encyclopedia entry9 August 2026

  Superficial Palmar Arch

  Embryologists have shown us that the hand is vascularized as follows: the median artery develops the earliest, followed by the interosseous, and this vessel is finally (and usually) replaced by the ulnar and radial arteries. These changes during development permit a wide range of vascular variations to occur. The mature arch supplied by a comes nervi mediani (median artery) represents a persistence of the earliest embryonal blood supply of the hand. The superficial palmar arch is subject to significant variations. The completion of the arch on the radial side is extremely variable.

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• Encyclopedia entry9 August 2026

  Deep Palmar Arch

  The deep palmar arch may be larger than usual, and its metacarpal branches may replace one or more of the common digital arteries by dividing at the cleft of the fingers into digital branches. The arch may be reinforced by enlarged posterior perforating branches from the radial and its branches on the back of the hand or by a large palmar interosseous. In some cases the radial joins the deep arch by passing through the second, instead of the first interosseous space.

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• Encyclopedia entry9 August 2026

  Bronchial Branches

  The bronchial arteries may arise from the internal thoracic, subclavian, inferior thyroid, supreme thoracic, thoracic aorta, abdominal aorta, costocervical trunk, or intercostal. It occasionally replaces a pulmonary artery. See also Thorax; Bronchial.

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• Encyclopedia entry9 August 2026

  Inferior Vena Cava

  The inferior vena cava, in cases of transposition of the viscera (0.2-0.5% of individuals), may lie on the left side of the aorta. It may also lie to the left of the aorta, without visceral transposition, crossing to the right to gain the caval opening immediately below the diaphragm. It may also cross over after receiving the the left renal vein. When the inferior vena cava is doubled, the left cava usually passes across the aorta into the right after receiving the left renal vein.

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• Encyclopedia entry9 August 2026

  Hemiazygos Veins

  The hemiazygos vein arises from one or more of three possible roots (lateral, intermediate and medial). The lateral root arises in 85% of individuals from the left subcostal and left ascending lumbar vein at the head of the twelfth rib. The intermediate root occurs in only 28% of individuals and arises from the dorsal side of the left renal vein. The medial root has an incidence of 40% and arises in a plexiform manner from small veins on the anterior side of upper lumbar veins and communicates with the inferior vena cava, renal vein, and possibly from the second and third lumbar segmental.

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• Encyclopedia entry9 August 2026

  Brachiocephalic Veins

  Quain found them extending well-up into the neck on the left side. Cooper (1832) and Gruber (1862) found that an innominate vein passed through the thymus gland in about 2% of their subjects. The brachiocephalic vessels may cross over the thymus gland. It is not unusual for these veins to receive cervical and / or accessory cervical veins. It is not extrordinary that bronchial veins may be tributaries of the vv. anonymae (innominate veins). They may pass behind the aorta.

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• Encyclopedia entry9 August 2026

  Ureteral Arteries

  The blood supply of the renal pelvis is usually from the renal arteries which form several anastomotic branches. The blood supply of the ureter may arise at its proximal end from the aorta or the renal, common iliac, or internal iliac arteries and reaches the ureter on its medial side, or it may arise from its distal end from a testicular or ovarian, vesical, uterine, or vaginal artery on its lateral aspect.

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• Encyclopedia entry9 August 2026

  Suprarenal Arteries

  In a classic study of the arteries of the suprarenal glands (111 cadaver dissections), it was concluded that the patterns of that gland's blood supply varies to such an extent that no two are ever alike. In another study (50 dissections), the suprarenal arteries were classified according to the part of the gland they supply. The superior suprarenal arteries supply the superomedial part of the gland, the middle suprarenal supplies the anteromedial part of the gland, and the inferior suprarenal supplies the posterior and the inferolateral aspect of the organ.

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• Encyclopedia entry9 August 2026

  Intercostal Artery

  The arteries of the first and second intercostal spaces usually arise from the superior intercostal branch of the subclavian, but occasionally the artery of the second space, and more rarely that of the first, may arise from the thoracic aorta. The arteries of the third and fourth intercostal spaces, as well as those of the first and second, may arise from the superior intercostal, the aortic intercostals being correspondingly reduced in number. Esophageal branches are found in 20% of humans, on the right side, arising from the fifth posterior intercostal artery.

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• Encyclopedia entry9 August 2026

  Thyroidea Ima (of Neubauer) Artery

  This artery occurs in from 4 to 10% and was briefly discussed with the brachiocephalic trunk. The frequency is not certain but appears to be about 10% according to most authors but Adachi found this artery in only 1 of 271 cadavers (0.4%). Thyroidea ima arises from any one of the following sources: aortic arch, brachiocephalic trunk, common carotid, internal thoracic, pericardiacophrenic, subclavian, thyrocervical trunk, inferior thyroid, or transverse scapular artery. It usually but not always arises from the right side.

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• Encyclopedia entry9 August 2026

  Tibial and Tibialis Anterior Arteries

  The tibial artery may be absent, its place being supplied by the peroneal. The tibialis anterior artery may take a course around the lateral side of the fibula and follow the lateral aspect of the leg. The anterior tibial may be absent, rudimentary, or highly developed. It may terminate at the lower limit of the leg and fail to join the dorsalis pedis artery, in which case the dorsalis pedis arises from the perforating branches of the peroneal artery.

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• Encyclopedia entry9 August 2026

  Anterior Communicating Artery

  This artery is occasionally doubled (7% of cases), and may exist in one of several patterns. In 50 brains, the anterior communicating artery had a diameter of 1.5 mm or less in 44%, and 1.0 mm or less in 16%. In one study of 1647 brains, the anterior communicating artery was so small in 6% of cases that it restricted circulation (from one side to the other) between two anterior cerebrals. The anterior communicating artery, contrary to many textbook descriptions, may not be oriented in a strictly transverse plane.

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• Encyclopedia entry9 August 2026

  Anterior Choroidal Artery

  This artery arises from the internal carotid in 85% of cases, middle cerebral in 8%, and the junction between these two vessels in 7%. It may be diminished or absent, replaced by a branch of the deep cerebral or posterior communicating artery.

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• Encyclopedia entry9 August 2026

  Anterior Cerebral Artery

  Both the right and left anterior cerebral arteries may run as one vessel to divide distally, or one may be a branch of the contralateral artery. In some instances the anterior cerebral arteries are united into a single trunk, like the basilar artery behind, and this again divides into the right and left arteries (4%).

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• Encyclopedia entry9 August 2026

  Common Carotid Arteries

  The right common carotid may be absent. The artery may obliquely cross the lower part of the trachea above the level of the sternum. This occurs on the right side when the right brachiocephalic is situated to the left of the midline, when the right common carotid arises as the second branch of the aortic arch, or when the right and left common carotids arise as common stem from the aorta. It occurs on the left side when the left common carotid arises from the brachiocephalic.

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• Encyclopedia entry9 August 2026

  Facial Artery

  The facial artery is frequently rudimentary. It may terminate as a submental artery, i.e., not reaching the face, or as a labial or alar nasi (lateral nasal) artery and not as the angular (43% of cases studied). In its absence, it may be replaced by the nasal branch of the ophthalmic artery at the medial side of the orbit, by the transverse facial or by the maxillary artery. The facial, when larger than usual may replace the frontal branches of the ophthalmic or the nasal artery, on the other hand the submental branch of the facial may arise from the lingual.

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• Encyclopedia entry9 August 2026

  Superficial Cervical Artery

  This artery may arise from a common stem with the suprascapular or from the transverse cervical. In some cases, it provides an accessory vertebral artery. The superficial cervical artery usually has the following four origins: 17% 64% 11% 8% From Dubreuil-Chambardel.

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• Encyclopedia entry9 August 2026

  Deep Cervical Artery

  There are several variations in this artery. It may be a branch of the supreme intercostal or internal thoracic, or it may join the vertebral above the atlas. When smaller than usual, its area of supply may be supplemented by branches of other regional vessels. The artery occasionally provides an accessory vertebral. It may be a branch of the vertebral, thyrocervical trunk, inferior thyroid, suprascapular, or transverse cervical.

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• Encyclopedia entry9 August 2026

  Vertebral Arteries

  The right vertebral artery may arise: a) from the first part of the subclavian, nearer than normal to the brachiocephalic (1% of cases) or to the anterior scalene muscle; b) directly from the arch of the aorta (3% of cases); c) from the right common carotid, when the right subclavian arises from the aorta beyond the left subclavian; or d) from the brachiocephalic trunk. The right artery may pass behind the esophagus. The left vertebral artery may arise directly from the left common carotid, or the root of the subclavian, close to the aortic arch. It may arise from the arch of the aorta.

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• Encyclopedia entry9 August 2026

  Superior Thyroid Artery

  This artery is generally considered to be always present , 100% (its absence however, has been reported once). The superior thyroid has been reported to give rise to a sizable branch that descends anterior to the clavicle and supplies the pectoralis major muscle. An unusually large superior thyroid may replace the contralateral vessel or the inferior thyroid artery on the same side. It can be so small that it is represented only by muscular branches or by the superior laryngeal artery.

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