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Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus III: Nervous System: Thoracic Spinal Nerves

Illustrated Encyclopedia of Human Anatomic Variation: Opus III: Nervous System

Thoracic Spinal Nerves

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

Peer Review Status: Internally Peer Reviewed

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.

The lateral branch of the second thoracic, the intercostobrachial (intercostohumeral) nerve, may divide into an anterior and posterior division. The anterior division may, however, be absent. In either case, the lateral branch anastomoses with the medial brachial cutaneous, usually with the lateral branch of the third intercostal, and rarely with the lateral branch of the first intercostal if it is present.

Frequency of Occurrence of the Lateral Cutaneous Branch of the First Intercostal Nerve. (after Tachibana and Miyauchi)


Frequency of Occurrence


No. found/No. body halves

Cave (1929)



Sato (1971)



Kasai/Chiba (1980)






The size of the intercostobrachial cutaneous nerve and the extent of its distribution are reportedly inversely proportional to the size of the other cutaneous nerves of the arm, especially the medial brachial cutaneous nerve. When the medial brachial cutaneous nerve is absent, it is replaced by the intercostobrachial nerve.

The first thoracic nerve may have no cutaneous branch. The sixth, seventh, and eighth nerves may provide cutaneous branches from both their lateral and medial branches. Thoracic spinal nerves supply the sternalis muscle, when present (3-5% of individuals), and the axillary arch muscle, when present.

Image 31A Image 31B Image 31C Image 31D Image 31E Image 31F

Image 31G Image 31H Image 31I Image 31J


Antonelli, G. (1879) Di una rara anomalia nella compoizione del plesso brachiale e di alcuni ganglii soprannumerarii nel corso dei sette ultimi nervi intercostali. Resoconto delle Adunanze e dei Lavori della Reale Accademia Medico-Chirurgica di Napoli. 33:195-201.

Bishop, W.E., Carr, B.W., Anson, B.J. and F.L. Ashley. (1943) The parietal intermuscular plexus of the thoracic nerves. Q. Bull. Northwestern University Medical School. 17:209-216.

Cave, A.J.E. (1929) The distribution of the first intercostal nerve and its relations to the first rib. J. Anat. 63:367-379.

Chetrick, A. and L.R.M. del Guercio. (1951) Unusual brachial plexus formation. Yale J. Biol. Med. 23:395-398.

Cunningham, D.J. (1877) Note on a connecting twig between the anterior divisions of the first and second dorsal nerves. J. Anat. Physiol. 11:539-540.

Cunningham, D.J. (1888) The musculus sternalis. J. Anat. Physiol. 22:391-407.

Davies, F., Gladstone, R.J. and E.P. Stibbe. (1932) The anatomy of the intercostal nerves. J. Anat. 66:323-333.

Kasai, T. and S. Chiba. (1980) Further observations on the cutaneous nerves to the upper arm arising from the medial cord of the brachial plexus. Acta. Anat. Nippon Tokyo 55:8-22. In Japanese with English abstract.

Kodama, K. (1986) Morphological significance of the supracostal muscles, and superficial intercostal nerve: A new definition. Acta Anat. Nippon, Tokyo 61:107-129. in Japanese with English abstract.

Kumaki, K., Yamada, M., Kumaki, S., Miaki< K., Kodama, K. and K. Kawai. (1979) The extramural nerves on the thoracic region Acta Anat. Nippon, Tokyo 54:226 In Japanese.

Lamont, J.C. (1887) Notes on the nervous supply of the musculus sternalis. J. Anat. Physiol. 21:514-515.

Minne, -., Senneville, _. and -. Libersa. (1949) Sur quelques particularités concernant la trajet et la distribution des nerfs intercostaux. Assoc. Anatomistes Comptes Rendus 36:492-496.

Miyauchi, R. (1982) A case having abnormal nerve supply of the external oblique abdominal muscle with anomaly of the intercostal nerve. Acta Med. Nagasaki. 27:130-141.

Miyauchi, R. (1983) Abnormal nerve supply of the musculus obliquus externus abdominis in man. Acta Anat. Nippon, Tokyo 58:513-525.

Sato, S. (1971) On the lateral cutaneous branch of first intercostal nerve, with special reference to the interrelation with the cutaneous nerve in arm. Hirosaki Igaku., Hirosaki 23:320-338. In Japanese with English abstract.

Schaefer, E.A., Symington, J. and T.H. Bryce., Eds. (1915) Quain's Anatomy, 11th ed., Longmans, Green, and Co., London.

Tachibana, G. and R. Miyauchi (1987) Nerve supply to and the true nature of anterior supracostal muscle: three cases of the anterior supracostal muscle innervated by the external muscular branch of the first intercostal nerve having lateral cutaneous branch. Anat. Anz. Jena 169:235-245.

Wilson, J.T. (1888) The innervation of axillary muscular arches in man, with remarks on its significance. J. Anat. Physiol. 22:294-299.

Wilson, J.T. (1913) The innervation of the achselbogen muscle. J. Anat. Physiol. 47:8-17.

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