Partial unilateral absence of the trapezius muscle in a human cadaver

We report here the partial unilateral absence of the trapezius muscle found during dissection. The left trapezius was significantly reduced in size when compared to the right trapezius, especially in its inferior third. Moreover, the existing fibers of the left trapezius inferior to the scapula were only one-third to two-thirds as thick as those on the right. The vertebral attachment of the inferior fibers of the left trapezius was also notably higher than that on the right. Morphometric analysis indicated that the surface area of the left trapezius was approximately 50% that of the right trapezius. Fiber orientation along the left and right trapezius muscles was also markedly different. An examination of nerve supply yielded no apparent anomalies, therefore suggesting that the absence of trapezius has a developmental etiology.