Three-dimensional structure of the perimysium in sternocleidomastoid muscle

The morphology of the sternocleidomastoid muscle (SCM) of human fetuses, ranged from 12 to 32 weeks gestation, was investigated by a light microscopy and a scanning electron microscopy. The collagenous fibers of the perimysium of the SCM formed complex structures from 24 weeks gestation by contrast to fibers of the endomysium of the SCM. The cross-sectional area (CSA) of the bundle of muscle fibers and the CSA of the individual muscle fibers of the SCM increased during development from 12 to 32 weeks gestation, in a process linked to the development of the perimysium. Therefore the perimysium affects and controls to the muscle fiber of the developed SCM and acts to resisting stretch forces in the movements. The changes in the arrangement and development of the collagenous fibers in the perimysium may be correlated to with these of the muscle fibers.