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Bilateral supernumerary clavicular head of the sternocleidomastoid muscle on a human fetus cadaver

MOJ Anatomy & Physiology
José Aderval Aragão,1,5 Weslley Hewesson Góes Cruz Modesto,2 Nilson César Menezes Santos,Iapunira Catarina Sant’Anna Arago,3 Felipe Matheus Sant’Anna Aragão,3 Paôla Cardoso,3 Fernanda Pimentel Cavaliere de Barros,3 Juliana Cardoso da Silva,4 Francisco Prado Reis5

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The sternocleidomastoid muscle (SCM) variations relating to its number of heads have been continuously reported, but the bilateral appearance is very rare. It is a flexor muscle of the neck and an accessory muscle for breathing, normally presents two heads, but multiple variations can occur, including one or more accessory heads. These, when present, could be one of the complicating factors of the central venous puncture, because of the narrowing in the minor supraclavicular fossa. Report the finding of bilateral supernumerary heads on the SCM of a human fetus. It was found a rare variation of the SCM with bilateral supernumerary heads on a 23,9weeks old male human fetus cadaver. The heads originated in the clavicules middle third, they were separated by a wider triangular space, when compared to the triangle formed between the usual sternal e clavicular heads, which corresponds to one more superficial depression, the additional minor supraclavicular fossa. On the right side, the heads united at the level of the hyoid bone to a distance of 22,65cm, and on the left, 20,22cm. The knowledge of the SCM possible anatomical variations is essentially important to vascular surgeons and anesthesiologists, who intervene on the minor supraclavicular fossa during the implantation of a central venous catheter, thus avoiding complications during the performance of procedures.


anatomical variation, neck muscles, peripheral nerves, skeletal muscle, sternocleidomastoid, sternal head, clavicular head, sternohyoid muscle, omohyoid muscle; Numbers 1-2 indicate the heads, sternocleidomastoid muscle