![]() The possible explanation in our case is that the same single matrix developed into the inferior belly of the omohyoid alone but not the SM and subclavius posticus. The coracoclavicular ligaments were also observed and appeared normal in morphology.ĭuring embryological development, there is a single mesodermal matrix for the development of the inferior belly of omohyoid, SM, and occasionally for the subclavius posticus muscle. These ligaments were very strong, unyielding to cuts and pressure applied by the forceps during the demonstration. The extent of the ligament from the costochondral junction to the coracoid process was observed bilaterally ( Figs. Also, noted bilaterally was the association with the thickened CCL. It was observed bilaterally that no accessory muscles were supplementing the absent SMs. During this step of the dissection, the absence of SMs bilaterally was noted. This was followed by the deep dissection extending up to the undersurface of the clavicle. The muscle was transected close to the origin and reflected laterally towards its insertion on the humerus, to expose the underlying pectoralis minor and clavipectoral fascia. Skin and subcutaneous tissues were dissected to identify the pectoralis major muscle. Keywords: Costocoracoid ligament, Subclavius muscleĭuring routine educational dissection of a male cadaver of 65 years of age, at the Department of Anatomy, All India Institute of Medical Sciences, New Delhi, a rare bilateral variation in the pectoral region was observed. This anatomical variation may be associated with thickened CCLs and can be correlated to the smooth functioning of the pectoral girdle. Absent SM may be due to anomalous development from the muscle matrix that also forms the inferior belly of the omohyoid apart from the SMs. Both SM and CCL help in the maintenance of smooth movements of the pectoral girdle and both may not always be present. ![]() Having similar attachments as the subclavius, the costocoracoid ligament (CCL) is the thickening of the proximal part of clavipectoral fascia extending up to the coracoid process. Subclavius muscle (SM) has a proximal attachment to the first costochondral junction and the muscle fibers are then directed upwards and laterally to get attached distally to the subclavian groove of the clavicle. Such variations are not uncommon in muscles, particularly in the upper limb. Anatomical variation is defined as normal flexibility in the topography and morphology of body structures.
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