Muscle spindle supply to the snout musculature in moles (Talpidae)

To define the anatomical background of the neuromuscular mechanism involved in the movement of the snout of the moles (Talpidae) the present histological study was carried out on the snout muscles of this family including the Japanese shrew-mole (Urotrichus talpoides), Japanese lesser shrew-mole (Dymecodon pilirostris) and Temminck's mole (Mogera wogura). The snout musculature consists of five muscles: A) Zygomaticus major, B) Levator labii superioris, C) Levator alae nasi superioris, D) Levator alae nasi inferioris and E) Zygomaticus minor, the former two of which are the possessor of the muscle spindles and the latter three of which are not so, with the exception of the Zygomaticus minor having one spindle in the Japanese shrew-mole. Seventy-three spindles were counted on one side of the snout musculature in the Dymecodon pilirostris (12 g in weight), 120 spindles in the Urotrichus talpoides (19 g in weight) and the Mogera wogura (100 g in weight). The snout musculature was 0.015 g, 0.02 g and 0.1 g in weight, respectively. The number of spindles per milligram weight of the muscle was 4.9 in the Dymecodon, 6 in the Urotrichus and 1.2 in the Mogera. The density of the spindle distribution was much higher in the former two than in the latter one. Since the Dymecodon and Urotrichus actually search for food by moving their long snout vigorously over the ground and the Mogera, being a subterranean, searches for food by moving his snout not so vigorously under the ground, the pattern of the snout movement seems to be coincident with the morphological differentiation of the snout musculature and the density of the muscle spindle distribution in the moles (Talpidae).