M. Articularis Coxae—a Possible Receptor Organ

The purpose of the study was to analyse the morphology of the equine m. articularis coxae with reference to its function during locomotion. The muscle was a constant finding in 50 horses of verying age nad sex. Different horses were selected for dissection of the muscle with its vessels and nerves, determining of length at different angles of the hip joint and weight. The muscle was shortest at maximal fexion, and the length incereased rapidly until a hip joint angle of 110°. Between 11° and maximal extension the increase in length was moderate. The mean weight of muscle was 2.7 g. Histological specimens were serially sectioned and the frequency of muscle spindles was recorded. The spindle density varied from 12 to 42 per gramme of muscel, with a mean of 26, and a mean length of the muscle spindles of 4.7 mm.
Myectomy was performed uni- or bilaterally on 5 horses to evaluate the influenceon the locomotion with no significant manges observed.
Considering the position, size, innervation and multitude of muscle spindles of the m. articularis coxae it is suggested that the muscle primarily has a receptor function inreporting on the torsion or "wrinkling" of the hip joint. The absence of manges in loconiotion of the myectomised horses indicates that the missing function of the muscle is taken over by other muscles.