The sternalis muscle (musculus sternalis) is the name usually given to this common anatomical variant, but the terms ‘episternalis’, ‘presternalis’, ‘sternalis brutorum’, ‘rectus thoracis’, ‘rectus sterni’, ‘superficial rectus abdominis’ and ‘japonicus’ have also been used in the literature (for reviews see Le Double, 1879; Calori, 1888; Pichler, 1911; Blees, 1968). According to Turner (1867), Cabrolius was the first, in 1604, to describe sternalis. Nevertheless this muscle is often unknown even in clinical practice (Bailey & Tzarnas, 1999; Vandeweyer, 1999). Thus far, investigations on the incidence of sternalis have been made both in large populations such as the American (Barlow, 1935) and small populations, for example in Taiwan (Shen et al. 1992; Jeng & Su, 1998). In Europe, all studies on the frequency of this muscle have been made amongst subpopulations in Western (e.g. Cunningham, 1888; Le Double, 1890, 1897) and Northern Europe (Gruber, 1860) although the reported frequencies have been quite different. There is a lack of information about sternalis in Eastern European populations. We therefore present data from a study on the incidence of sternalis muscle in Bulgaria.

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In order to study the incidence of the axillary arch in the Bulgarian population, we examined the axillary regions of 56 formol-carbol fixed human cadavers and observed two cases with a unilateral axillary arch. In the first case, the variant structure was situated on the right side of a 58-year-old female cadaver. The axillary arch extended from the lateral border of the latissimus dorsi to the posterior layer of the pectoralis major tendon. In the second case, the axillary arch was found on the left side of a 63-year-old male cadaver and had the same attachment points as in the first case. The innervation and blood supply of the arches are discussed. We have also reviewed extensive information concerning the clinical importance of the axillary arch, and for the first time, it was summarized clearly for clinicians. The summary consists of three parts: "diagnosis" of the axillary arch by physical investigation or imaging techniques; the axillary arch and surgical interventions in the region of the axilla; the axillary arch as an entrapment site for the axillary vessels and nerves.

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Since the definition of supraclavicular nerve entrapment syndrome by Gelberman et al. (Gelberman et al. [1975] J. Bone Joint Surg. Am. 57:119) a number of clinical cases of this specific entrapment neuropathy have been reported. In all these cases, the nerve injury has been attributed to the location of the supraclavicular nerve branch in a narrow canal in the clavicle. However, in the anatomical literature, variations in the course of the supraclavicular nerves have not only been ascribed to bony canals but also to abnormal fibrous and muscular structures. Considering the fact that the existence of a narrow site with rigid walls along the course of a nerve is essential for the development of an entrapment neuropathy, our study examines all the variant anatomical structures with a possible role in supraclavicular nerve entrapment. We describe three groups of anatomical structures with close relation to the course of the supraclavicular nerves-transclavicular canals, fibrous bands, and unusual muscular structures. Based on the characteristics of the variations found, for the first time, we suggest that in addition to the bony canals through the clavicle certain fibrous and muscular structures could also be an anatomical basis for supraclavicular nerve entrapment syndrome.