Variation archive

854 published articles

• Encyclopedia entry9 August 2026

  Esophageal Arteries

  "The pharynx, esophagus and trachea are usually supplied by several very fine arterial twigs from the terminal branches of the inferior thyroid artery. Although these arterial branches are quite small in size, they are usually multiple in number, ranging from 1 to 4 on either side.These branches may pass directly to the esophagus and trachea, or may pursue a long and devious course downward into the superior mediastinum, before breaking up into their terminal branches.

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• Encyclopedia entry9 August 2026

  Renal Arteries

  Renal artery variations including their number, source, and course are very common. Irregularites of the renal vessels are found in about 35% of cases studied. The most common is the presence of an additional vessel (~28%). So-called accessory arteries arising above the usual trunk is more frequent than one arising below. Supernumerary vessels are more frequent on the left side than the right. It is not only ludicrous but dangerous to suggest that the kidneys each receive only a single artery.

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• Encyclopedia entry9 August 2026

  Radial Artery

  The radial artery may arise from the brachial more proximal than usual (approx. 1inch (2.54 cm) in every 8 cases studied), from the axillary artery, or from the brachial lower than the bend of the elbow although a low division of the brachial is rare. Tiedemann found a case where the radial arose below the upper third of the forearm. It may run superficial to the fascia of the forearm. In some cases it crosses over, instead of under, the extensors of the thumb.

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• Encyclopedia entry9 August 2026

  Axillary Artery

  The major variations of the axillary artery are discussed here; there are many! Occasionally, it gives rise to the radial artery or, more rarely, to the ulnar artery. Still more rarely, it gives rise to the interosseous artery or a vas aberrans. It may give rise to a common trunk from which may arise the subscapular, anterior and posterior circumflex humeral, profunda brachii, and ulnar collateral arteries. The branches of the brachial plexus may surround this common trunk, but not the main brachial artery.

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• Encyclopedia entry9 August 2026

  Subclavian Arteries

  Variations of the subclavian artery are also considered along with variations of the aortic arch (listed under AORTA). Irregularities in the major branches of the aortic arch have been classified by Poynter as follows: 1). Branches fewer than usual as in the occurrence of bi-innominate arteries; 2). branches more numerous than usual, as in the absence of the innominate, and consequent separate origin of both carotid and subclavian arteries; 3). branches in abnormal succession, dependent upon an irregular development of the usual aortic-arch plan.

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• Encyclopedia entry9 August 2026

  Internal Carotid Artery

  The internal carotid rarely provides branches in the neck. However, the ascending pharyngeal, occipital, transverse facial, and lingual arteries, as well as a laryngeal and a meningeal artery, have all been reported to arise from the internal carotid prior to its entry into the carotid canal. The internal carotid may take a sinuous course with a pronounced curve or a horseshoe shape, or may even form a complete loop in the upper cervical part of the vessel. This kinking of the artery may be due, however, to cardiovascular disease. This artery is occasionaly absent uni- or bilaterally.

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• Encyclopedia entry9 August 2026

  Aorta: Arch and Thoracic part of the Descending Aorta

  The aorta may vary in its position and extent without any other irregularities. The height of the arch may be as high as the level of the third dorsal (thoracic) vertebra or as low as the fifth thoracic. The summit of the arch may reach the top of the sternum. The distance that the aorta extends downward depends on the point of its division into the common iliac arteries. The point of the division may be as high as the third lumbar vertebra (in some rare cases higher) or as low as the fifth lumbar vertebra.

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• Encyclopedia entry8 August 2026

  Triceps Brachii

  Variations in the triceps are neither numerous or common. Each of the heads may be fused, in varying degrees, with neighboring muscles. The fibers of the long head may be found extending to the capsule of the shoulder joint above or distally, for a greater extent than usual on the axillary border of the scapula. Macalister (1875) described the variations of triceps extensor cubiti (triceps brachii) as follows: 1.

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• Encyclopedia entry8 August 2026

  Trapezius

  Like the sternocleidomastoid, the trapezius is a compound muscle consisting of three distinct parts, as indicated by a more or less clear separation of the clavicular portion of the muscle from the rest and, less frequently, by the separation of the lower from the middle portion. The three parts consist of 1) a dorsoscapularis superior, 2) a dorsoscapularis inferior, and 3) a cleidooccipitalis division.

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• Encyclopedia entry8 August 2026

  Transversus Thoracis Anterior (Sternocostalis) and Subcostalis

  Transversus thoracis arises from the posterior surface of the sternum and xiphoid (to the level of the third costal cartilage) and extends onto the internal surface of the second (third) to sixth costal cartilages. Transversus thoracis may extend to the first rib. Absence on one or both sides has been recorded. It is sometimes divided into separate fasciculi which may number from two to six, and its division into two lamellae has also been observed. This muscle was Hyrtl's candidate for the most variable in the body.

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• Encyclopedia entry8 August 2026

  Transversus Perinei Superficialis

  This muscle is frequently absent or poorly developed. Sometimes it consists of several separate fasciculi, and it may be inserted wholly or in large part into the bulbocavernosus or external anal sphincter. A muscular slip is occasionally found arising from the fascia at the lower border of gluteus maximus or upper fascia lata and inserts under the origin of bulbocavernosus in the albuginea of the bulbous (penile) urethra in males. This variation is not found in females.

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• Encyclopedia entry8 August 2026

  Transversus Abdominis

  The number of costal slips varies: it may be reduced to five or increased to seven. The muscle has been fused with internal oblique; it has also been reported absent. Absence of the inguinal bundles has been reported; on the other hand, extension of the transversus to the pubic crest has also been noted, and the spermatic cord has been seen piercing its lower border. The insertion onto the seventh rib may be absent, but in some cases there may be a supernumerary digitation for the sixth rib.

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• Encyclopedia entry8 August 2026

  Transpleuralis

  Muscular bands have been reported in the oblique fissure of the right lung, which originate from the sixth rib and extend to the central part of the diaphragm just behind the caval opening. Reference Allen, L. (1950) Transpleural muscles. J. Thoracic Surg. 19:290-291.

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• Encyclopedia entry8 August 2026

  Tibialis Posterior

  Variations of this muscle are few and rare. At least two cases have been reported in which the muscle consisted of two parts; the accessory part was inserted separately in the sole of the foot. The insertion onto the first cuneiform may be absent. Macalister reported the variations of the tibialis posterior as follows: 1. It may have a trifurcated tendon, one slip going to the usual site of insertion, the second to the tendon of peroneus longus, and the third to the heads of the third and fourth metatarsal bones; 2.

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• Encyclopedia entry8 August 2026

  Tibialis Anterior

  The tendon may be found divided, for a variable distance proximally, into a cuneal (reference os cuneiform) and metatarsal slip; in very rare instances, this division may involve the whole muscle. In some cases, a deep division of the tendon has been found inserted onto the talus (m. tibioastragalus of Gruber) , and the tendon may also supply a slip to the head of the first metatarsal or base of the first phalanx. A separate muscular slip, tibiofascialis anticus , sometimes occurs.

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• Encyclopedia entry8 August 2026

  Thyroarytenoideus and Vocalis

  A superior thyroarytenoideus muscle, in the form of a thin band, arises from the inner, anterior superior surface of the thyroid cartilage and crosses the cartilage and thyroarytenoideus, inserting on the inferior lateral aspect of the arytenoid cartilage of the larynx. The portion of vocalis that inserts onto the the vocal ligament has been designated the aryvocalis (Ludwig) muscle.

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• Encyclopedia entry8 August 2026

  Teres Minor

  Absence of teres minor has been reported. Teres minor may be absent in 4% of individuals (Mori, 1964). The partial separation into two parts has also been reported; one inserted onto the the greater tubercle and the other onto the neck of the humerus (teres minimus scapulae [Gruber]). The origin of the muscle may be expanded so that it covers the infraspinatus entirely replacing the fascial sheet (deep fascia) usually covering that muscle. Teres minor may fuse with infraspinatus in 20% of cases studied (Mori).

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• Encyclopedia entry8 August 2026

  Teres Major

  It is believed that this muscle is closely related developmentally with latissimus dorsi. It is part of the same muscle sheet and it is often fused with a slip of latissimus dorsi at the inferior angle of the scapula. A muscular slip has been found joining the scapular head of the triceps, as well as one joining the fascia of the (upper) arm on its lateral aspect. An accessory slip originating from the vertebral border of the scapula just below the spine has also been described. The tendon of insertion is variable.

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• Encyclopedia entry8 August 2026

  Tensor Fasciae Latae

  This muscle is occasionally found doubled longitudinally, partially or completely. Accessory slips have been reported proceeding from the iliac crest, inguinal ligament, or aponeurosis of the abdominal wall. Union with gluteus maximus has been observed. This muscle is considered by some authors to be an atrophied relic of a "deltoid" of the hip. The muscle may be absent. The tensor fasciae latae and the gluteus maximus represent separated portions of a muscle known as the ilio-tibialis in reptilia (Iguana).

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• Encyclopedia entry8 August 2026

  Supraspinatus

  The supraspinatus is very constant in form and attachments. Macalister called the muscle singularly invariable. However, very rare variations include the following: a) the division of its belly into two parts, b) an additional slip that arises from the suprascapular ligament, c) a connection between its tendon and that of pectoralis minor, d) a slip passing from its tendon to that of pectoralis major or to the pectoral ridge of the humerus, and e) attachment to a tendinous lamella below the insertion of pectoralis major on the humerus. Syn.: m. Obergrätenmuskel, Sus-épineux.

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