In mammals, the Musculus quadriceps femoris is a well-developed extensor muscle of the thigh. It is also relatively well developed in bats. The muscle group consists of a distally elongated muscle belly, which is important for the full extension of the knee joint during terrestrial locomotion. However, most bats species demonstrate poor terrestrial locomotion, although several species are able to crawl on the ground. Among the crawling bats, knee joint extension is necessary for crawling. Among bat species generally, the M. quadriceps femoris has a distally elongated belly for extending the shank, although the feature also occurs among poor crawling bat species. The relationship between a relatively well-developed M. quadriceps femoris and poor crawling ability in bats is incongruous, but there is a possibility that bats with a reduced M. quadriceps femoris have not yet been found. The greater horseshoe bat (Rhinolophus ferrumequinum) has long been known to be incapable of crawling, but there are no detailed descriptions in the literature concerning this bat’s M. quadriceps femoris. The findings of this study reveal that the M. quadriceps femoris of Rh. ferrumequinum has a short muscle belly attached to the proximal portion of the femur; furthermore, the insertional tendon of this muscle and its patellar ligament are very thin. These morphological features suggest that this species cannot exert a strong and long-distance extension of its knee joints, unlike most other bat species. In addition to the above described morphological features, the M. rectus femoris of Rh. ferrumequinum is fused with the vasti in the M. quadriceps femoris. This M. quadriceps femoris arises from the pelvis and inserts onto the femur. Therefore, Rh. ferrumequinum has an M. quadriceps femoris specialized for flexion of the hip joint.
KEY WORDS: Rhinolophus ferrumequinum; Musculus quadriceps femoris; Patellar ligament.