Functional strategies of the hindlimb muscles in the mouse deer

Abstract

We observed the muscles of hindlimb, talus, and tarsal joints in the lesser mouse deer (Tragulus javanicus) and greater mouse deer (Tragulus napu) that have conserved the original morphological characters of the musculoskeletal system in the Ruminantia. The proximal trochlea articulating to the distal end of the tibia obviously turned at a medio-proximal direction. Since the proximal parts of the muscle bundles were concentrated in the lateral side of the thigh, the tension of the extensor muscles in the hindlimb is medio-distally conducted. It indicates that the extending power of hindlimb muscles is not parallel with the direction of the trochlea, but crosses the angle of the proximal pulleys in the talus. We suggest that the crossing may enable the animal to stand and run stably and to bear its body weight. We compared the development of the hindlimb muscles in the mouse deer (Tragulus javanicus and Tragulus napu) with that in the Sika deer (Cervus nippon) and Chinese muntjac (Muntiacus reevesi). The dry weight of the muscles in the mouse deer indicated that the mass of the muscles were obviously concentrated in the lateral side of the proximal area and in the cranial side in the distal area in comparison with the two other large-bodied species. We can conclude that the present findings of the hindlimb muscles and talus in the mouse deer indicate the original functional strategy of the locomotion in non-specialized species of the Suborder Ruminantia.