Ferret deep hip and tail muscles
Photos and Text: Catherine Lenox and Victoria Clayton
| Muscle | Origin | Insertion | Action |
| Quadratus lumborum | Centra of posterior thoracic and lumbar vertebrae, sometimes lower ribs | Ilium | Bends the body laterally |
| Psoas major | Lumbar vertebrae | Lesser trochanter of femur | Flexes hip |
| Psoas minor | Centra of posterior thoracis and anterior lumbar vertebrae | Ilium | Flexes back |
| Iliacus | Deep surface of ilium | Lesser trochanter of femur | Flexes hip |
| Gemellus superior | Ilium and ischium | Greater trochanter of femur | Rotates and abducts leg |
| Obturator internus | Ischial ramus | Trochanteric fossa of femur | Abducts leg |
| Quadratus femoris | Ischial tuberosity | Lesser trochanter | Retracts and rotates leg |
| Gemellus inferior | Lateral surface of ischium | Tendon of obturator internus | Abducts leg |
| Obturator externus | Pubis and ischium | Trochanteric fossa of femur | Rotates and protracts leg |
Adapted from Klingener (1979)
The tail of the ferret is used for maintaining balance. Female ferret tails
contain eighteen vertebrae [1] and range in length from seven to fourteen centimeters
[2]. This variation in tail length is most likely attributable to differences
in body length, which varies from 20.5 to 38.5 centimeters [2]. This particular
ferret's tail was about ten centimeters in length. It was one centimeter in
diameter at the base and tapered to about one quarter of a centimeter at the
tip.
We began this dissection by skinning the tail of the ferret. We also removed the remaining lumbodorsal fascia from the base of the tail. This fascia is very thick and was difficult to remove. This fascia is similar in function to the retinacula of the manus and ankle; it serves to brace the tendons of the sacrospinalis muscle at the base of the tail. The tendons of the sacrospinalis are embedded in this tough fascia and are difficult to separate from the fascial layer.
The sacrospinalis muscle fuses in the lumbodorsal region, about three centimeters cranial to the base of the tail. The fused sacrospinalis muscle becomes tendinous at the base of the tail and the tendons continue along the dorsal aspect of the tail. These tendons lie superficial to a thin layer of intrinsic epaxial tail musculature. The ventral side of the tail is composed of a thin layer of undifferentiated hypaxial musculature [3].
The ferret tail muscles are less differentiated and much smaller than those of the fox. The fox uses its tail for balance and communication, and so the tail must have a wide range of motion. The tail muscles are large and differentiated to provide this range of motion. The sole function of the ferret tail is balance, and therefore its range of motion is much smaller and the muscles do not need to be highly differentiated.
We removed the entire left half of the urogenital system to expose the left psoas muscles. The psoas major is superficial to and shorter and narrower than the psoas minor. The psoas major originates from the lumbar vertebrae dorsal to the diaphragm. It is approximately seven millimeters thick. The muscle fibers of the psoas major become tendinous at the length-wise midpoint of the psoas minor. The psoas minor is dorsal to, longer than, and twice as thick as the psoas major. The psoas minor originates cranial to the origin of the psoas major at the anterior lumbar vertebrae and inserts at the ilium. The cranial origin of the psoas minor allows it to function in back flexion, while the caudal insertion of the psoas major muscle reflects its role as a hip flexor.
The ferret psoas muscles are very long, which is expected in an animal with such a long body. However, even when total body length is taken into account, the psoas muscles in the ferret are relatively longer than those in the fox and cat. The thickness of the psoas muscles also varies across species; the ferret's are thin relative to the rabbit's. The long, thin psoas muscles seen in the ferret reflect its long, thin body type.
We reflected the gluteus maximus, gluteus medius, and femorococcygeus to reveal the deep hip flexors. The deep hip flexors include the gemellus superior, obturator internus, quadratus femoris, gemellus inferior, and obturator externus. The quadratus femoris is the most distal deep hip flexor. This muscle is much shorter than the other hip flexors and is just proximal to the adductor magnus and distal to the gemellus inferior. It originates at the ischial tuberosity and has a broad insertion into the lesser trochanter of the femur. The quadratus femoris retracts and rotates the leg.
The gemellus inferior is just proximal to the quadratus femoris. This is the broadest and shortest of the deep hip flexors. It originates at the lateral surface of the ischium and has a broad insertion on the tendon of the obturator internus, another deep hip flexor. The obturator nerve crosses over the gemellus inferior. Both the gemellus inferior and the quadratus femoris are deep to the femorococcygeus.
Both the gemellus inferior and the obturator internus abduct the hip. The obturator internus is anterior to the gemellus inferior and is deep to the gluteus maximus. It is longer and narrower than both the gemellus inferior and the quadratus femoris.
The gemellus superior is anterior to the obturator internus, posterior to the gluteus medius, and deep to the gluteus maximus. It is approximately the same size and shape as the obturator internus. Its insertion into the greater trochanter of the femur is just proximal to the insertion of the obturator internus into the trochanteric fossa. The gemellus superior abducts the hip and rotates the leg.
1. Fox, J.G. 1998. Biology and Diseases of the Ferret (2nd Ed.). Williams & Wilkins, Baltimore.
2. Nowak, R.M. 1999. Walker's Mammals of the World (Vol. 1) (6th Ed.). Johns Hopkins University Press, Baltimore.
3. Romer, Alfred Sherwood. 1962. The Vertebrate Body, Third Edition. W.B. Saunders Company, Philadelphia and London. 627 pp.
4. Klingener, D. 1979. Laboratory Anatomy of the Mink (2nd Ed.). William C. Brown, Dubuque, Iowa.