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Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: B:

Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: B

Biceps Brachii

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD

Peer Review Status: Internally Peer Reviewed

This muscle is very variable. In about 12% of arms, a humeral head is found in addition to those usually found arising from the coracoid process (medial or short head) and the glenoid lip of the scapula (lateral or long head). A biceps with more than two heads is found in about 8% of Chinese, 10% of white Europeans, 12% of Black Africans, and about 18% of Japanese.

A biceps may be composed of 1 to 5 heads. In one small study of 18 subjects, an accessory head was found six times, and a fourth head was found once. The variations appeared three times on the right side, two times on the left and one time on the both sides.The most common accessory slip is one arising from the humerus at the insertion of coracobrachialis, extending between it and the brachialis muscle. It joins the short head, but most of its fibers join the semilunar fascia. It may be isolated and terminate entirely in the fascia. Mori described various origins of the third or accessory head as follows: In 50 arms there were 10 (20%) arms with a third head of the biceps. The origins of these additional heads were:

  1. The distal portion of the deltoid tuberosity, 4 arms, 8%.
  2. Near the point of the humeral insertion of coracobrachialis, 3 arms, 6% and
  3. The terminal tendon of pectoralis major, 2 arms, 4%.

The two other accessory heads are rare and take several different forms. When fully developed, they arise close together from the neck of the humerus, below the lesser tubercle and behind the pectoral tendon to which they may be more or less joined. The more lateral of the two slips joins the long head of the muscle, whereas the medial joins the short head.

In other instances, the two heads of the biceps muscle may be totally separate or fused and either head may be absent. In the absence of the long head, the tendon may be found arising from the bicipital groove, one of the tubercles, the capsule of the joint, or the tendon of pectoralis major. The tendon may be doubled or it may be represented only by the lacertus.

The lacertus, which may be doubled, may compress the median nerve as found in the anterior interosseous nerve syndrome. An accessory slip may arise from the deltoid muscle. At the distal end of the biceps muscle, various muscular or tendinous slips have been described connecting biceps to the lower end of the humerus, the ulna, radius, antebrachial fascia, or neighboring muscles. Thereby, supernumerary heads may also arise from brachialis, brachioradialis, or the fascia or fibers of the pronator teres muscle. da Silva Leal summarized the entire literature to 1926 and reported that supernumerary heads of the biceps occur in about 10% of individuals (148 reports in 1453 individuals).

Also a fleshy slip may also arise from the medial border of biceps and pass to the medial intermuscular septum or medial epicondyle over the brachial artery. The brachial artery may actually pass through this slip or its tendon. This is a potential entrapment site for the brachial artery. Other fascicles have been reported passing to brachialis, pronator teres, flexor carpi radialis, flexor digitorum profundus, or to the lateral side of brachioradialis.

The long head of biceps may be perforated by a duplicated musculocutaneous nerve.

Macalister (1875) reported the variations of biceps brachii as follows;

  1. The muscle may be entirely suppressed;
  2. The short head may be absent (Meckel);
  3. The long head was found deficient by Otto, Lauth, Henle, Hyrtl, and Macalister;
  4. The fascial insertion was found to be absent in one arm (Macalister);
  5. The radial insertion has been found absent by Petit (1733) and Haller (1768);
  6. The same, with an insertion into the elbow capsule and the coronoid process, was found in a case of congenital absent of the radius by Gruber;
  7. The two heads of the muscle may be separate for the entire length of the muscle (Maclaister); a similar case is reported by Riverius (1545); in another case the muscle was split for three-fourths of its course;
  8. The long head was found doubled by Moser;
  9. I have found the long head arising from the capsular ligament;
  10. Or from the bicipital groove;
  11. A doubled coronoid head was described by Wood and by Macalister;
  12. This anomalous portion may join the main body of the muscle, or else it may unite with the normal coracoid head before that portion of the biceps joins the long head;
  13. An extension of the coracoid head from the coracoacromial ligament was found six times by Macalister, other cases by Wood;
  14. Macalister reported a slip to the short head from the insertion-tendon of pectorlis minor;
  15. The most common of all varieties of this muscle is the occurrence of a third head, and the most frequently present third head is that from the interval between the coracobrachialis and brachialis anticus (brachialis): the frequency of this variation depends upon the author: Theile, once in nine; Hallett, once in fifteen; Wood, eighteen out of one hundred and seventy-five subjects, and Macalister found it once in ten subjects;
  16. Macalister found a third head arising directly from the brachialis anticus (brachialis). This third head Macalister found crosses the brachial artery (and may compromise it) has also been seen by Quain and Struthers and others; In Struthers' case the muscle covered the artery by a tendinous arch;
  17. A separate slip from coracobracialis continuous with the short head is described by Mr. Wood and Macalister;
  18. A humeral head starting from the insertion of coracobrachialis is reported by Macalister, but it is not as frequent as that arising fron brachialis;
  19. A third head may arise between the insertion of the deltoid and the origin of supinator longus (brachioradialis);
  20. This has been found as a separate muscle, distinct for its whole length, as far as its insertion from the biceps, and is described with the brachioradialis (Gruber, 1848), Theile, Hyrtl. Wagner; Wood and Pietsch describe it as imperfectly separate;
  21. A head like 19 above, but continuous with deltoid has been found by Macalister;
  22. In another similar case Macalister found the usual long head absent;
  23. The same variation may join supinator longus (brachioradialis) instead of deltiod;
  24. A variety of internal third head (15 above), is described by Hyrtl, is that in which the accessory part arises from the internal intermuscular septum;
  25. An instance of the origin of the long tendon of the biceps from the tendon of pectoralis major is described by Koster;
  26. A third head from from the outer lateral tuberosity is described by Meckel;
  27. The long head may attach to the greater tuberosity of hunerus;
  28. 28. Haller describes a third head arising from the outer margin of the bicipital groove by a tendon;
  29. 29. Macalister found an accessory third head arising from the upper border of pronator teres and inserted with the biceps;
  30. A series of four heads was found by Macalister with a usual third humeral origin coexisting with a head from the great tuberosity similar to 26 above;
  31. Wood found a four headed muscle, in which the lateral and menial humeral origins coexisted (15 and 19 above);
  32. Another quadricipital arrangement has been seen by Macalister, where the short head was doubled, and the medial humeral head (15) coexisted with the greater tuberosity head (26) but without the long tendon;
  33. Henle found a quinqueceps (five headed), the normal heads and the third humeral head coexisting with one from the deltoid, and a fifth from the middle of the bicipital groove as high as the tendon of pectoralis major;
  34. In another four-headed biceps which Macalister found ,the two normal heads, and the medial humeral coexisted with an origin from the outer (lateral) lip of the bicipital groove;
  35. Meckel (1826) described a biceps consisting of a short and a humeral head;
  36. Of unusual insertions, Macalister notes a slip from the lateral head inserted separately into the radius is one of the rarest of these (reported by Sels, 1815) and by Rudolphi;
  37. A normal-arising biceps was seen by Mr. Wood to have three insertions- an outer normal portion, giving off a radial tendon and a superficial semilunar fascia; a middle smallest portion was inserted into the fascia, over supinator brevis (supinator) and the bursa of the radial tuberosity; the inner division, which ended in a strong trifurcating tendon, sent a slip to the coronoid origin of the pronator teres, one into the coronoid insertion of brachialis, and one into the coronoid attachment of flexor sublimis;
  38. Kelly found a small tendon detached from the lower end of the biceps, giving origin to part of the flexor carpi radialis;
  39. A slip from biceps to the internal intermuscular septum is described by Quain;
  40. Kelly reported that there arose from the long head of an otherwise normal biceps a tendinous slip, which becoming fleshy, was inserted at the lowest part of the antecubital fossa, by three tendons, one into the fascia over the supinator longus (brachioradialis), a second into the semilunar fascia, and the third dipped into the bottom of the fossa between pronator teres and the supinator muscle;
  41. In a somewhat similar case the muscle (40 above) was inserted by two slips-one into the bursa over the tubercle of the radius under the normal tendon, and the other, into the coronoid process;
  42. Another, and larger accessory biceps muscle is described by Pietsch, which arose by three heads-one from the lateral side of the humerus, one from the medial side of the humerus, and one from the short head of the biceps itself; these three were inserted by a separate tendon into the radius at its tubercle behind the ordinary biceps tendon;
  43. Macalister reported a slip from the biceps to brachialis anticus, running downwarsds and a little inwards;
  44. Theile described a tricipital muscle in which there were two coracoid heads, and a slip from the capsular ligament with no long head;
  45. Macalister found one biceps, which inserted by four slips, besides the normal insertion, to the internal (medial) brachial ligament, to the capsule of the elbow joint, to the coronoid process, and to the pronator teres;
  46. The slip which, arising from the biceps and crossing the brachial artery, is sometimes traceable down as far as the fascia over the pronator teres, is described by Struthers as a "brachio-fascialis;" it is also illustrated by Quain;
  47. A simple fascicle of the biceps inserting into the origin of the pronator teres Macalister has seen three times. It is also described by Clason of Upsala;
  48. Gruber found in a case of deficient radius a biceps possessing a weak coracoid head, two humeral origins, and two insertions-one radial and one ulnar. The absence of biceps brachii has also been reported.
Syn.: m. flexor radii, flexor antibrachii radialis, Zweikopfiger Armmuskel, Speichenbeuger, Biceps Huméral (Cruveilhier).

Image 140

Split Terminal tendon of Biceps and Palmaris Longus Variation.
from Calori, 1867.

Image 134

Third Head of Biceps Brachii.
from Barrett.

Image 44

Third Head of Biceps Brachii.
from Calori, 1866a.

Image 33

A Humeral Third Head of Biceps Brachii.
source unknown to authors.

Image 170

Fourth Head of Biceps Brachii.
source unknown to authors.

Image 231

Fifth Head of Biceps Brachii.
from de Burlet and Correlijé.

Image 43

Irregular Muscle Attachments Located on the Humerus.
from Jackson.

Image 47

Irregular Muscle Slip Joining Biceps Brachii Arising from the Brachial Fascia Covering Triceps Brachii.
The muscular slip crosses over the median nerve, the brachial artery, and the superior ulnar collateral artery. This arrangement may compromise the functioning of nerve and arteries.
from Calori, 1868.

Image 20

Third Head of Biceps Brachii with Accessory Bicipital Aponeurosis.
Slightly modified from Spinner, Carmichael, and Spinner.

Image 72

Expansive Lacertus Fibrosus Entrapping the Ulnar Artery.
from Calori, 1866a.

Image 176

Union between Biceps Brachii and Pronator Teres.
Source unknown to authors.


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