KOLLIKER, A. On the termination of nerves in muscles, as observed in the frog ; and on the disposition of the nerves in the frog's heart. Proc Roy Soc B. 1862, 12, 65-89
KUHNE, W. Ueber die Endigung der Nerven in den Muskeln. Arch Prth Anat Physiol. 1894, 27, 508-523
SHERRINGTON, CS. On the anatomical constitution of nerves of skeletal muscle ; with remarks on recurrent fibers in the ventral spinal nerve-root. J Physiol. 1894, 17, 211-258
COOPER, S. The responses on the primary and secondary endings of muscle spindles with intact motor innervation during applied stretch. Quart J Exp Physiol. 1961, 46, 389-398