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

Adapted from Klingener 1979.

We began this dissection by removing the skin from the lower back and the right leg. There is a layer of fascia and fat underneath the skin we removed as well.

We easily identified the gracilis and sartorius, the superficial muscles of the medial aspect of the thigh. The sartorius is a broad muscle, though it is not very thick. This muscle is the anterior part of the medial side of the thigh. It wraps around the anterior part of the femur and is visible as the anterior margin of the lateral side. The gracilis is as broad and thick as the sartorius but is only visible on the medial side. It makes up the posterior compartment of the medial side of the thigh.

The sartorius is innervated by the femoral nerve. This nerve is clearly visible and is contained in the femoral sheath with the femoral artery and vein. The sheath runs in a groove between the gracilis and sartorius muscles, superficial to the adductors before passing through the adductor hiatus in the adductor magnus. The gracilis is innervated by the obturator nerve [1], which we did not see.

We used a dull probe to separate the muscles of the lateral side of the thigh. The superficial muscles of the lateral side include the biceps femoris, the tensor fascia lata, the gluteus maximus, the femorococcygeus, and the semitendinosus. A thin section of the sartorius can also be seen. The biceps femoris is by far the largest muscle of the thigh. This fan-shaped muscle has a narrow origin at the ischium and a broad insertion on the lateral surface of the knee and leg. The tensor fascia lata is composed of only a small amount of muscle. The tendon of the tensor fascia lata must be severed to reveal the vastus lateralis, which runs deep to this muscle. The gluteus maximus is the most proximal of the thigh muscles and is bordered posteriorly by the femorococcygeus and anteriorly by the tensor fascia lata. The femorococcygeus is directly caudal to the gluteus maximus. The fibers of the femorococcygeus and the gluteus maximus form a v-shaped pattern and the muscles can be differentiated based on the direction of their fibers. The fibers of the femorococcygeus run anterior and distal, while the fibers of the gluteus maximus run posterior and distal. These muscles are similar in size and function. The semitendinosus is only visible in the proximal half of the posterior compartment of the thigh. The remaining part of the muscle is covered by the biceps femoris.

After identifying all of the superficial muscles of the thigh, we reflected the biceps femoris and tensor fascia lata to observe the deeper muscles. We cut the sciatic nerve when we reflected the biceps femoris and then removed a large layer of fat that was directly underneath this muscle. The tenuissimus, also known as the abductor cruris caudalis in the ferret [1], is a long, thin muscle just deep to the biceps femoris. It runs from the lumbodorsal fascia to the lateral surface of the leg. We unintentionally cut this muscle when we reflected the biceps femoris. After we reflected the superficial muscles, we could see the deep muscles of the lateral side of the thigh. These include the semitendinosus, the semimembranosus, the presemimembranosus, and the vastus lateralis. The lateral edge of the adductor magnus, a medial deep muscle, is also visible on the lateral side. The semitendinosus, semimembranosus, and presemimembranosus make up the posterior compartment of the lateral deep muscles of the thigh. They are all approximately the same size. These three muscles, along with the biceps femoris, make up the hamstrings. The semitendinosus, semimembranosus, and biceps femoris are "two-joint" muscles that cross both the knee and hip joint [2]. The presemimembranosus only crosses the hip joint. We reflected the tensor fascia lata to reveal the vastus lateralis, the anteriormost deep muscle of the lateral side of the thigh. This muscle is the broadest and thickest of the deep muscles on the lateral side. This muscle is one of the four muscles that make up the quadriceps. The other three are the vastus medialis, the vastus intermedius, and the rectus femoris.

After completing the deep dissection of the lateral side, we proceeded to the medial side. We reflected the sartorius and gracilis to reveal the deep muscles. We used a dull probe to separate the muscles so we could identify them. The semitendinosus, the semimembranosus, and the presemimembranosus have large cross sectional areas and are clearly visible on both the medial and lateral side of the thigh. The other deep muscles on the medial side include the adductor magnus, the adductor brevis, and the adductor longus, the pectineus, the vastus medialis, and the rectus femoris. The adductors are the narrowest and shortest of the deep muscles, and the adductor magnus is the largest of this group of muscles. The adductor hiatus allows the femoral artery and nerve to pass through the adductor magnus. It is located in the center of the belly of this muscle. The adductor brevis, the shortest of the adductors, is partially fused to the anterior side of the adductor magnus, making it difficult to differentiate the two muscles. The adductor longus is narrower than the other adductors and is anterior to the adductor brevis. The pectineus, an extremely short and narrow muscle, is anterior to the adductor group and posterior to the vastus medialis. The pectineus is the fourth adductor muscle of the thigh. The rectus femoris and the vastus medialis make up the anterior compartment of the lateral deep muscles of the thigh. They run along the anterior side of the femur. They are of similar size and form a v-shaped pattern with the other deep muscles of the medial side. The vastus medialis is posterior to the rectus femoris, which is the anteriormost muscle of the lateral side of the thigh.

There are several differences between the ferret's and other quadrupedal carnivores' thigh musculature. The cat, for example, has a fused presemimembranosus and semimembranosus, and this larger muscle is also partially fused with the adductor group. Cats also have a completely fused adductor brevis and adductor magnus instead of two partially fused muscles. The fox has one large adductor muscle instead of three smaller ones. Although we cannot know for sure which adductor muscle arrangement is primitive and which is advanced, the different degrees of fusion of these muscles suggest that the adductor muscle group is one that has evolved significantly over time.

References

1. Fox, J.G. 1998. Biology and Diseases of the Ferret (2nd Ed.). Williams & Wilkins, Baltimore.

2. Klingener, D. 1979. Laboratory Anatomy of the Mink (2nd Ed.). William C. Brown, Dubuque, Iowa.

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