Tree shrew thigh
Photos and Text: Terence Mitchell
Removing the skin - Peel the skin covering the lower limb from an existing edge using the rat-tooth forceps. The skin should come off easily, leaving only a layer of deep fascia. Create a small hole with the sharp probe, and then insert the probe between the fascia and muscle to separate the two as much as possible. Repeat this process to create several large breaks in the deep fascia. Remove the remaining tissue with forceps.
Note: The superficial muscles, gluteus maximus and femorococcygeus, are visible in the uppermost photo. The deeper muscles, gluteus medius, piriformis, gluteus minimus, and caudofemoralis, are visible in the middle photo.
Gluteus maximus - Arises from the ilium and lumbocaudal fascia and inserts in to the fascia lata and third trochanter. Gluteus maximus is superficial, large, and hard to miss. Cut its superior attachments and reflect. Extends and laterally rotates the thigh at the hip joint.
Femorococcygeus - Arises from the transverse processes of caudal vertebrae and inserts laterally on the femoral shaft and third trochanter. This muscle is tightly fused to the inferior border of gluteus maximus. Extends the thigh at the hip and flexes the leg at the knee.
Gluteus medius - Just deep to gluteus maximus, this large muscle arises from the ilium, iliac crest, and lumbocaudal fascia and inserts along the femur from the greater trochanter to the third trochanter. Reflect this muscle laterally. Abducts and medially rotates the thigh.
Piriformis - Arises from the sacrum and ilium and inserts on the greater trochanter deep to gluteus medius. Look for this muscle along the inferior border of gluteus medius. Extends and laterally rotates the thigh.
Gluteus minimus - Arises from the gluteal surface of the ilium inferior to the origin of gluteus medius and inserts on the greater trochanter. This muscle is much smaller than and deep to gluteus medius. Abducts and medially rotates the thigh.
Caudofemoralis - Arises from the transverse processes of the caudal vertebrae and inserts on the medial side of the distal femur. Look for this muscle deep to femorococcygeus. Extends the thigh at the hip. Note that the sciatic nerve emerges between the caudofemoralis and piriformis. Before reaching the gastrocnemius it branches into a tibial nerve supplying the anterior compartment of the shank and a common fibular nerve to the posterior and lateral compartments of the shank.
Note: Vastus lateralis and biceps femoris are both visible in the uppermost photo, while rectus femoris is visible in the lowermost. Tenuissimus is just barely visible in the middle photo, attached to the deep fibers of biceps femoris.
Vastus lateralis - Arises from the anterior aspect of the greater trochanter and inserts on the patella. Look for this superficial muscle distal to gluteus maximus. Extends the leg at the knee joint.
Rectus femoris - Arises from the anterior inferior iliac spine and acetabular rim and inserts on the patella. Look for this muscle just medial to vastus lateralis. Extends the leg at the knee joint. This muscle also crosses the hip joint and helps flex the thigh.
Biceps femoris - Arises from the ischial tuberosity and inserts on the patella and tibial crest. Look for this superficial muscle just posterior to femorococcygeus. Cut the distal attachments and reflect. Extends the thigh at the hip and flexes the leg at the knee.
Tenuissimus - Arises from the lumbocaudal fascia and inserts on the patella and tibial crest. Look for this muscle deep to biceps femoris. Extends the thigh at the hip and flexes the leg at the knee.
Note: Most of the medial thigh and iliopsoas muscles are visible in the lowermost photo. Vastus intermedius cannot be seen because it is deep to vastus medialis. It may also be difficult to discriminate between adductor longus and pectineus in the picture, because these muscles are small, partially bound by fascia, and difficult to reach.
Gracilis - Arises from the inferior pubic ramus and inserts on the tibial crest. This is the most superficial muscle of the medial thigh and is fused with sartorius distally. Adducts the thigh at the hip joint and flexes the leg at the knee joint.
Sartorius - Arises from the tendon of the external oblique and inserts on the tibial crest. Flexes, laterally rotates, and abducts the thigh at the hip joint. This muscle also crosses the knee joint and helps flex the leg.
Vastus medialis - Arises from the medial aspect of the femur from the greater to lesser trochanter and inserts on the medial side of the patella. Look for this muscle just medial to rectus femoris. Cut the proximal attachments and reflect. Extends the leg at the knee joint.
Vastus intermedius - Arises along the anterior of the femoral shaft and inserts on the patella. Look for this muscle deep to vastus medialis. Note that it is much smaller than either vastus medialis or intermedius. Extends the leg at the knee joint.
Semitendinosus - Arises from the transverse processes of the caudal vertebrae and ischial tuberosity, and inserts on the tibial crest deep to gracilis. Look for this muscle posterior to biceps femoris. Extends the thigh at the hip and flexes the leg at the knee.
The next five muscles form approximately parallel bands in the medial thigh. I will list these structures beginning with the most distal and moving proximally.
Semimembranosus - Arises from the ischial tuberosity and inserts along the knee joint. Extends the thigh at the hip and flexes the leg at the knee.
Adductor magnus - Arises from the inferior pubic ramus and inserts on the third trochanter and distal femoral shaft. Adducts and extends the thigh at the hip joint. Although the femoral artery was inadvertently destroyed before I could photograph it, I will attempt to reconstruct its course through prior personal observations, and past dissections [1]. The femoral artery emerges dorsal to the inguinal ligament superficial to iliopsoas. It gives off a few small branches and then dives through the adductor hiatus of the adductor magnus muscle. At this point it gives rise to an artery supplying the hamstrings, and a separate branch, which follows the tibial nerve.
Adductor brevis - Arises between the pubic ramii and inserts on the medial aspect of the femur. Adducts the thigh at the hip joint.
Adductor longus - Arises from the superior pubic ramus and inserts with adductor brevis on the femur. Adducts the thigh at the hip joint.
Pectineus - Arises from the superior pubic ramus and inserts along the posterior femoral shaft. Helps adduct and flex the thigh at the hip joint.
Iliacus - Arises from the transverse processes of the lumbar vertebrae and inserts on the lesser trochanter. Flexes the thigh at the hip joint with psoas major and psoas minor.
Psoas major - Arises from the lumbar vertebrae and inserts on the lesser trochanter. This muscle is fused with iliacus to form the iliopsoas inferiorly. Flexes the thigh at the hip joint with psoas minor and illiacus.
Psoas minor - Arises from the lumbar vertebrae and inserts on the ilium. Flexes the thigh at the hip joint with psoas major and illiacus.
As noted above, the muscles of the thigh and gluteal region are responsible for extension, flexion, abduction, adduction, and rotation of the thigh and in some cases the shank. Therefore, these muscles are critical to the proper functioning of the leg during locomotion. Tupaiid locomotion was studied intensely because of its potential usefulness as a model for early therian biology [2]. Such studies use cineradiographic techniques to investigate the movement of skeletal elements during locomotion on treadmills. In a recent study Schilling and Fischer examined the kinematics of walk, trot, and gallop gaits in a male and female common treeshrew, Tupaia glis [3]. The data show that tree shrews increase speed from walk to trot gaits by increasing step frequency. Due to a lack of data for gallops, and the animals' inability or unwillingness to perform bounds on the treadmill, it could not be determined how speed increases for the in-phase, bound and gallop, gaits. This is a fairly common result as many animals fail to perform normally on treadmills [4]. Tree shrews resemble other small mammals in that their humerus and tibia are horizontal to the ground when their foot is up, and their femur is horizontal when their foot is down [3]. Additionally, tree shrews maintain their ulna in a horizontal plane when their forefoot is down. Such limb geometry during symmetrical gaits allows for the full length of the structure to contribute to extension, and allows for a crouched posture. Crouching gives animals a greater ability to maneuver and increases stability. T. glis is similar to other small mammals in the degree to which the scapula contributes to overall body propulsion, total length that a fixed point on the animal moves over one stride. The scapula contributes a surprisingly high 40-60% of total propulsion length. This large contribution seems to be part of a general trend in small mammals towards dominance of proximal limb segments to stride length. The contributions of the humerus and ulna are highly variable and dependent on gait. The hand contributes significantly more to overall body propulsion relative to other small mammals. The contributions of hindlimb segments are also variable across gaits due to the added extension from the lumbar vertebrae during galloping. The movement of the femur and foot contribute significantly more to total stride length relative to other small mammals. While there are minor differences all tree shrews share important locomotor traits such as contributions of the spine to propulsion, flexed limb posture, and dominance of proximal segments to overall propulsion. In contrast they show few locomotor similarities to primates [5].
1 Le Gros Clark, W.E.1926. On the anatomy of the pen-tailed tree shrew (Ptilocercus
lowii). Proceedings of the Zoological Society of London 1926: 559-567.
2 Jenkins, F.A. 1974. Tree shrew locomotion and the origins of primate arborealism.
In: F.A. Jenkins, ed.: Primate Locomotion. New York: Academic Press. pp. 85-115.
3 Schilling, N. and M.S. Fischer. 1999. Kinematic analysis of treadmill locomotion
of tree shrews, Tupaia glis (Scandentia: Tupaiidae). Z. Saugetierkunde.
64: 129-153.
4 Barrey, E., P. Galloux, J.P. Valette, B. Auvinet, and R. Wolter.. 1993. Stride
characterstics of overground versus treadmill locomtion. Acta. Anat. 146:90-94.
5 Whitehead, P.F. and S.G. Larson. 1994. Shoulder motion during quadrupedal walking in Cercopithecus aethiops: Integration of cineradiographic and electromyographic data. J. Hum. Evol. 26:525-544.
Davis, D.D. 1938. Notes on the anatomy of the tree shrew Dendrogale.
Field Mus. Publ. Chicago Zool. 20:383-405.
George, R.M. 1977. The limb musculature of the Tupaiidae. Primates 18:1-34.
Le Gros Clark, W.E.1924. The myology of the tree shrew (Tupaia minor).
Proceedings of the Zoological Society of London 1924: 559-567.
Le Gros Clark, W.E.1926. On the anatomy of the pen-tailed tree shrew (Ptilocercus lowii). Proceedings of the Zoological Society of London 1926: 559-567.