Scapular insertion of the rabbit latissimus dorsi muscle: Gross anatomy and fibre-type composition

This paper defines the characteristics and significance of the scapular ins ertion of the latissimus dorsi muscle (LDM) of the rabbit. In a study of th e New Zealand White species (n = 10) the scapular insertion was found to be a consistent anatomical feature of the LDM that made up 12.3% (+/-2.3) of the total muscle weight. The fibres arise from the medial aspect of the bod y of the LDM and run in a caudocranial direction to be inserted into a broa d, thin tendon beneath the scapula ridge. This is morphologically different from the scapular component of the human LDM which is a well-recognized bu t inconsistent feature and consists of no more than a small leash of fibres running around the lower pole of the scapula. The scapular insertion was d eeper red in colour than the body of the muscle and fibre-typing demonstrat ed a mean slow-fibre composition of 49% (+/-2.6) compared to 16% (+/-1.7) f or the body of the muscle (p < 0.01). Mapping of the fibre types throughout the remainder of the LDM confirmed that the body of the muscle was of fast phenotype but with significantly more slow fibres in the superomedial segm ent of the muscle than elsewhere. This region of the muscle contributes mai nly to the scapular insertion and it is proposed that this part of the musc le takes on a predominantly postural role in stabilising the scapula during movement of the forelimb. Copyright <(c)> 2001 S. Karger AG,Basel.