Lab instructions:

For this lab, teams will focus primarily on dissecting the muscles of the proximal pelvic limb on the caudal and medial aspects, in canine and feline cadavers. This carnivore understanding can then be applied to the prosected large animal cadavers to identify the same muscles (and any extras) as directed.

Before we dissect, a reminder from the Thoracic Limb section:

What do we mean by muscle attachments?

All muscles have attachments. In most instances, the more proximal attachment is considered the origin. The insertion is the more distal attachment, and this end is the limb part that typically moves the most when the muscle contracts. The origin is usually a direct attachment of the muscle cells to the bone. For our purposes, you are not responsible for learning which attachments are the origin versus the insertion.  At times, however, you may be asked for the distal or proximal attachment of a muscle or muscles.  The insertion often is by a tendon or aponeurosis extending from the muscle cells to the bone. A tendon consists of dense, regularly arranged fibrous connective tissue organized into a small, well-defined bundle. An aponeurosis has the same consistency as a tendon, but the fibrous tissue is arranged as a thin sheet of tissue (i.e. take a round-bodied tendon and flatten it out with a rolling pin like dough rolled out for a pie crust, and you have made an aponeurosis!). A ligament typically refers to dense fibrous connective tissue between bones, and the term is also used for a variety of thin fibrous connections between organs or between an organ and the body wall.

MUSCLE CHARTS:  You are responsible for knowing the attachments and action(s) of muscles as described in the muscle action charts.  Use additional information in the following descriptions as a reference.

As always, read before you continue dissection! In many instances, during the study of muscles, a description of a specific muscle will be given before the instructions for dissection. Follow instructions as carefully as possible. In each instance clean the exposed surface of the muscle being described, isolate its borders, and verify its attachments. If the muscle is to be “transected,” free it from underlying structures first. As each muscle is defined, try to visualize its attachments and position on the skeleton and understand its function.

Ready? Then lets go!  All muscle dissection is performed on the left side of the body.

The following muscles will be dissected in this lab:

Caudal thigh

• Biceps femoris m.

• Semitendinosus m.

• Semimembranosus m.

Medial thigh

• Sartorius m.

• Gracilis m.

• Pectineus m.

• Adductor m.

Comments on fascia

There are superficial and deep fasciae of the pelvic limb. They cannot always be separated, and, in general, the deep fascia is more dense than the superficial fascia.

The superficial fascia of the trunk continues dorsally on the pelvis as the superficial gluteal fascia. In obese specimens, much fat is present between this fascia and the deep fascia.

A thick deep fascia covers the dorsal muscles of the lumbar area, pelvis, and tail. Called the thoracolumbar fascia (we have already met this fascia in previous sections), it is well developed in the lumbar region and is continued caudally at the iliac crest by the deep gluteal fascia. This distinct glistening fascia covers the muscles of the pelvis and serves in part as origin for the middle and superficial gluteal mucles. The deep gluteal fascia is continued caudally on the tail by the deep caudal fascia. The latter follows the irregularities of the caudal muscles and closely binds these to the vertebrae of the tail.

Distally, the deep gluteal fascia blends with the fascia of the thigh, where it becomes the medial and lateral femoral fasciae. The medial fascia is thin, whereas the lateral femoral fascia, also known as the fascia lata, is thick and serves as an aponeurotic insertion for thigh muscles. The femoral fascia is continued on the leg as the crural fascia.

Caudal muscles of the thigh – carnivore dissection

The caudal thigh muscle group consists of three primary muscles: the biceps femoris, laterally; semitendinosus, caudally; and semimembranosus, medially. (A fourth muscle, the slender caudal crural abductor muscle is closely associated with the caudomedial surface of the biceps femoris. It is of passing interest only.)

Biceps Femoris m.

The biceps femoris m. is the longest and widest of the muscles of the thigh. The biceps femoris m. attaches proximally on the lateral aspect of the tuber ischii and the sacrotuberous ligament that extends from the tuber ischii to the sacrum. NOTE:  The cat does not possess a sacrotuberous ligament. The sacrotuberous ligament will be dissected later in canine cadavers, with the lateral muscles of the pelvis.  Cranially and distally, the biceps femoris m. inserts by means of the fascia lata and crural fascia. Caudally, a band of heavy fascia extends from the biceps femoris m. to the tuber calcanei and helps to form the common calcaneal tendon.

The lymph node, typically surrounded by fat tissue, at the caudal border of the biceps femoris m. directly caudal to the stifle, is the popliteal lymph node.

The proximal attachments of the biceps femoris will be more apparent after lateral pelvic muscles are dissected.

PROXIMAL ATTACHMENTS: Sacrotuberous ligament in canine (sacrosciatic in ungulates) and ischiatic tuberosity

DISTAL ATTACHMENTS: Lateral stifle, tibia and tuber calcanei

ACTION: Flex the stifle; extend the hip (Secondary: extend stifle and tarsus, abduct hip)

Semitendinosus m.

The semitendinosus m., near its proximal attachment, lies between the biceps femoris and semimembranosus mm. Near its distal attachment it lies on the medial head of the gastrocnemius m. and is covered by the gracilis m.. The muscle extends principally from the ischiatic tuberosity to the tibial body. By means of the crural fascia, it also attaches to the tuber calcanei, contributing to the common calcaneal tendon.

PROXIMAL ATTACHMENT: Ischiatic tuberosity (all species) plus vertebrae and sacrosciatic lig. (horse and pig)

DISTAL ATTACHMENT: Tibia and tuber calcanei

ACTION: Flex the stifle; extend the hip. (Secondary: extend the tarsus)

Semimembranosus m.

The semimembranosus m. is greater in the transverse sectional area than the semitendinosus but is not as long. It is wedged between the semitendinosus and biceps femoris laterally and the gracilis and adductor medially. It has two bellies of nearly equal size (do not separate these). This short, thick muscle extends from the ischiatic tuberosity to the medial side of the distal end of the femur and the proximal end of the tibia. The insertions may be seen more adequately after the sartorius and gracilis muscles have been dissected.

PROXIMAL ATTACHMENT: Ischiatic tuberosity

DISTAL ATTACHMENT: Distal femur and medial condyle of the tibia

ACTION: Flex the stifle; extend the hip. (Secondary: extend the stifle)

Medial muscles of the thigh – carnivore dissection

Sartorius m.

The sartorius m. consists of two straplike parts in the canine that lie on the cranial and craniomedial surfaces of the thigh. These parts extend from the ilium to the tibia. The cranial part forms the cranial contour of the thigh and is relatively thick. The caudal part is on the medial side of the thigh and is thinner, wider, and longer than the cranial part. Both muscle parts lie predominantly on the medial side of the large quadriceps femoris.  In the feline, the sartorius m. is not subdivided into two bellies.

PROXIMAL ATTACHMENT: Ilium

DISTAL ATTACHMENT: Cranial part: patella; Caudal part: tibia

ACTION: Flex the hip (Secondary: cranial part extends the stifle; caudal part flexes the stifle)

Gracilis m.

The gracilis m. arises from the symphysial tendon, a thick, flat tendon attached ventrally to the pelvic symphysis (ventral midline of pelvis). The proximal aponeurosis of the gracilis covers the adductor.

PROXIMAL ATTACHMENT: Pelvic symphysis

DISTAL ATTACHMENT: Tibia and tuber calcanei

ACTION: Adduct the pelvic limb (Secondary: flex the stifle, extend hip and tarsus)

Pectineus m.

The pectineus m. is a small, spindle-shaped muscle that belongs to the deep medial muscles of the thigh. It lies between the adductor caudally and the vastus medialis belly of the quadriceps femoris m. cranially. It has a proximal attachment on the prepubic tendon and iliopubic eminence. There is a small cartilage embedded in the iliopubic origin.

PROXIMAL ATTACHMENT: Ilium and pubis

DISTAL ATTACHMENT: Distomedial femur

ACTION: Adduct the pelvic limb

Adductor m.

The adductor m. consists of two muscle bellies (adductor magnus et brevis and adductor longus) that are often not clearly divisible, and we do not attempt to separate them. It is a large pyramidal muscle compressed between the semimembranosus and pectineus, and it extends from the pelvic symphysis to the caudal aspect of the femur. It is partly covered by the biceps femoris laterally and gracilis medially.

PROXIMAL ATTACHMENTS: Pelvic symphysis, ischium and pubis

DISTAL ATTACHMENT: Distocaudal femur

ACTION: Adduct the pelvic limb (Secondary: extend the hip)

Now that we have dissected the medial muscles of the thigh an anatomical feature, the femoral triangle, should be viewed and understood (and it will be revisited in future units).

Femoral Triangle

The femoral triangle is a ‘space’, bound mostly by muscles, through which the blood vessels run to and from the pelvic limb. It is located on the proximal medial surface of the thigh with its base at the abdominal wall (at the level of the vascular lacuna). The triangle is bound by the sartorius cranially and the pectineus and adductor caudally. The iliopsoas and rectus femoris (to be dissected) form the proximal lateral surface of the triangle. The vastus medialis forms the distal lateral part. This triangle contains, among other structures, the prominent femoral artery and vein and the saphenous nerve.  In some specimens, the femoral nerve also may be observed in the femoral triangle as it emerges from the iliopsoas muscle.

Ungulate comparative anatomy

Croup versus Rump

The same area is referred to as the croup in the horse, and the rump in ruminants and the pig.

Caudal muscles of thigh

In the ruminant and pig (artiodactyls), the superficial gluteal muscle combines with the biceps femoris muscle to form a large muscle mass, the gluteobiceps muscle. In the horse the superficial gluteal m. remains separate from the biceps femoris m.

The gluteobiceps m. in artiodactyls has a cranial and caudal division in the biceps femoris part of the muscle.  In the horse, the biceps femoris m. has three divisions: cranial, middle, and caudal.  The divisions in the biceps are most notable distally.  Caudal to the biceps muscle mass, the semitendinosus m. and semimembranosus m. are present.  These latter two muscles have different proximal attachments in the horse and pig (ischium and vertebrae) versus the ruminant (ischium only), which accounts for the rounded croup of the horse and rump of the pig, versus the angular rump of the ruminant.

Medial muscles of the thigh