Purpose:

To learn to identify the muscles of the frog, To learn the action for each muscle. To compare the muscles of the frog to the muscles of the human.

Data:

Skin Removal   Use the diagram to begin removal of the frog skin. After removing the skin around the trunk, continue to remove the skin from the head and legs. The skin around the hind legs can be pulled off like a sock. Be careful not to tear any muscle tissue.

Dorsal Muscles

The Muscles of the Head

Muscles of the dorsal surface of the head act on the jaws.  The temporalis inserts on the lower jaw anterior to the jaw joint.  The depressor mandibulae attaches onto the end of the mandible posterior to the joint.

Major muscles of the shoulder, the dorsalis scapulae and the latissimus dorsi extend from the dorsal part of the trunk, or scapula, across the shoulder joint to the proximal end of the humerus. Two powerful, longitudinal muscles on the back, the longissimus dorsi and iliolumbaris, lie dorsal and lateral to the vertebral column, which they help to brace.  Posterior to them, a coccygeoliliacus extends between the ilium and urostyle. 

The anterior portion of the thigh is covered by a large muscle mass which can be divided into three parts - the glutaeus magnus (vastus externus), the tensor fasciae latae (rectus anticus) and the cruralis (vastus internus).  The first two parts arise from different parts of the ilium; the cruralis from the connective tissue capsule of the hip joint.  The tensor fasciae latae attaches to the other two, which in turn insert together onto the prosimal end of the tibiofibula.  For this reason, they are sometimes described as separate heads of a single muscle, the triceps femoris. 

The rest of the dorsal surface of the thigh is occupied by a slender biceps femoris ,  a large semimembranosus, and a gracilis minor.  All of these arise from the posterdorsal portion of the pelvic girdle and insert upon the prosimal end of the tibiofibula. 

The large calf muscle on the shank is the gastrocnemius. It arises by means of two large tendons from the distal end of the femur, and terminates in the powerful Achilles tendon. The peroneus has a rather long tendon which crosses in front of the knee joint. The other end of the peroneus attaches at the distal end of the tibiofibula.

Use the Dissection Works computer program to identify each muscle in the diagram below.

The mylohyoid extends transversely on the ventral surface of the head.

On the ventral surface of the body, the deltoid and the pectoralis extend from the trunk, or girdle, to the humerus.  The anconeus (triceps brachii) which is situated on the dorsal surface of the humerus, also crosses the elbow joint. A longitudinal rectus abdominis, located on each side of the midventral line, forms the ventral portion of the abdominal wall.  The rest of the abdominal wall is formed by two thin sheets of muscles, the external oblique and transverse, whose fibers run nearly perpendicular to each other. 

The most superficial muscle on the ventral surface of the thigh is the sartorius, a broad muscle extending diagonally from the anteroventral part of the pelvic girdle to insert upon the proximal end of the tibiofibula. A large adductor complex, consisting of the adductor longus and the adductor magnus, lies on either side and partly beneath the sartorius. A gracilis major, which is partly covered by the gracilis minor, lies posterior to the adductor magnus.  It arises from the posteroventral portion of the pelvic girdle and, with the gracilis major, inserts on the proximal end of the tibiofibula. The tibialis anticus longus attaches at the knee and the diatal end of the tibiobifula.

Use the Dissection Works computer program to identify each muscle in the diagram below.

1. Skeletal muscles are called voluntary muscles. Explain what you think this means.
2. Muscles work in opposing pairs to bring about movement. What does this mean? Give an example of muscles that oppose each other.
3. What are flexors? Extensors? Abductors? Adductors?