For comparison, see dissections of a cat, a ferret, a fox, a rabbit, and a tree shrew.

The epidermal layer of the leg was removed from the lower abdomen to the knee, both ventrally and dorsally. Whereas the brachium of Tadarida braziliensis consists of long bones with slender muscles, the leg has more bulbous musculature at the proximal thigh. In terrestrial mammals, these leg muscles play an important function in locomotion. Through research and exploratory dissection, we found that the leg muscles in bats play an equally important role in the locomotion of flight.

After we removed the epidermal layer of the thigh, we were able to observe the superficial muscles of the ventral and dorsal sides. On the ventral side, we then cut the gracilis muscle and reflected it to see the deeper and smaller muscles, such as the adductor group of muscles. The deeper the muscles on the thigh, the smaller they tend to be, and the muscle body lies proximally on the femur. Dorsally, cut the large gluteus maximus muscle distally at the tendon and reflected it to observe the small and bulbous gluteus medius muscle that is deep and proximal on the femur.

Points of Note:

Bats hang upside-down to sleep and nest during the day. Their knees are everted to aid with the grasping of the branch by their feet. (see Shank and Pes lab for foot specialization.) This is an important specialization in bats that re-orients the placement of the entire leg. In order to clarify the positions of the muscles in this lab, the term "ventri-medial" is used to encompass the muscles such as the adductor group and gracilis muscles. In humans these muscles are more medial. The term "dorsi-lateral" is used to encompass the gluteus and quadriceps groups.

Several thigh muscles that are common in mammals, are absent in Tadarida (gemellus inferior, biceps femoris, fused vasti- see below for specific notes). Therefore, in general the thigh musculature is reduced. It is logical that this musculature is reduced because the bat's primary mode of locomotion is flight, which requires mostly arm and upper body musculature. Some thigh muscles still are important for flight, as is mentioned later; however, compared to terrestrial mammals, bats need generally less musculature in their legs.

However, it is also important to note that bats are also efficient terrestrial locomoters, able to run very quickly over uneven surfaces. Recurved claws, in addition to flexible wrist and ankle joints, allow them to maintain traction on almost any type of substrate. The bat pes is naturally dorsiflexed and inverted during running, which may be vestigial in this bat, a remnant from tree-dwelling ancestors.

When the skin was removed, there were significant layers and pockets of fat in between the leg muscles. All previous dissections of this specimen yielded very little fat deposits on the other sections of the body. This is an unusual find, as perhaps bats tend to store the fat resources in their legs opposed to other parts of the body. However, this has not been confirmed by any literature.

Dorsi- lateral side

The biceps femoris muscle is absent in the bat genera Myotis and Hipposideros, and is vestigial in Macrotus. Of published bats, it is only present in Eumops, where it acts to extend the femur and flex the shank.[1] Upon dissection, no evidence of the biceps femoris was found, indicating that Tadarida braziliensis also lacks this muscle.

In bats, the quadriceps femoris consists of only two heads: vastus lateralis and rectus femoris. The vastus lateralis is actually composed of what was probably vastus lateralis, vastus medialis, and vastus intermedius, now fused together.[1]

Ventri- medial side

The gracilis muscle is the most superficial on the ventral side of the leg. It is a prominent muscle, thick and running from the pubic spine to the medial surface of the tibia approximately one third of the way down the tibia distally. In Eumops and Myotis (and probably Tadarida), gracilis maintains partial flexion of the shank against the pull of the plagiopatagium during flight. This action is also important in fully spreading the uropatagium and stabilizing the proximal portion of the plagiopatagium. Also, when locomoting with hind claws on a substrate, gracilis and semitendinosus act to extend and adduct the femur.[1]

We noticed in our dissection that the adductor femoris is divided into two parts: adductor magnus, and adductor brevis which is a common separation to all bats and many other mammals. It is interesting to note that in Tadarida braziliensis, the adductor brevis extends the femur, whereas in other genera, this muscle acts to adduct the femur. Most bats must keep the legs together when flying in order to streamline their bodies. However, in bats which have a uropatagium, such as T. braziliensis, the legs must extend in order to keep this flying surface taut.[1]

Pectineus aids in supporting the weight of the body during terrestrial locomotion, and acts with the other adductors to stabilize the femur during flight.[1]

We were not able to locate the gemellus inferior muscle in our dissection and found reference that this muscle is absent in Myotis. It may, therefore, also be absent in Tadarida.

Muscles of the Leg in Tadarida braziliensis mexicana:

REFERENCES:

1. Vaughan, T.A. 1970. "The Muscular System", [ 1, p. 139-194 in Wimsatt, W.A. (ed.) Biology of Bats: Vol. 1. Academic Press, New York.

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