Anthropomorphology of sternocleidomastoid muscle

This paper present descriptive and metrical investigations of the sternocleidomastoid muscle. The studies were carried out on 54 human fetuses in the age from 12 to 24 weeks of intrauterine life. The observation results are presented against the background of the most frequent varieties of this muscle in the Primates. The muscle most frequently consisted of 2 heads: the sternal and the clavicular heads which terminated with a very wide attachment on the cranium--from the posterior edge of the external acoustic foramen to the plane of symmetry on the occiput. Very frequently the muscle heads were double or even triple or fourfold due to the occurrence of additional muscle bands. In several cases ther occurred the Wood's cleido-occipital muscle. The analysis of the metrical characteristics of the muscle has shown that in the investigated developmental period, the muscle attachments significantly increase, particularly between the 4 and 5 months. The increase of the width of muscle attachments is the consequence of the increase in the dimensions of the corresponding parts of the skeleton testified by the high correlation coefficients. No statistically confirmed dimorphic and asymmetric differences in the dimensions of muscle attachments have been found.