The two heads are separated by a triangular surface depression, the lesser supraclavicular fossa. As they ascend, the CH spirals behind the SH and blends with its deep surface below the middle of the neck, forming a thick rounded belly to gain attachment to the lateral surface of the mastoid process through a strong tendon, and to the lateral half of superior nuchal line through an aponeurosis.
These additional heads made the SCM muscle thick and bulky to an extent that caused extreme reduction in the size of the lesser supraclavicular fossa. The left SCM was found to be without any variation.
Since the SCM is used as a myocutaneous flap in various graft surgeries (8,9) and the lesser supraclavicular fossa is utilized for central venous access (10), these variations must be kept in mind while approaching the region to avoid complications.
The two clavicular heads of origin of sternocleidomastoid muscle were separated by a wider triangular interval (compared to the interval between the sternal head and normal clavicular head), which corresponds to one more surface depression, the additional lesser supraclavicular fossa
. The additional slip is also supplied by a branch from the spinal part of the accessory nerve.