Experiment 27.  With the head slightly bent forwards, grasp between the fingers of the right hand the edge of the left sterno-cleido-mastoid, just above the collar bone.  Raise the head and turn it from left to right, and the action of this important muscle is readily seen and felt.  In some persons it stands out in bold relief.

Experiment 28.  The tendons which bound the space (popliteal) behind the knee can be distinctly felt when the muscles which bend the knee are in action.  On the outer side note the tendons of the biceps of the leg, running down to the head of the fibula.  On the inside we feel three tendons of important muscles on the back of the thigh which flex the leg upon the thigh.

Experiment 29. To show the ligamentous action of the muscles. Standing with the back fixed against a wall to steady the pelvis, the knee can be flexed so as to almost touch the abdomen.  Take the same position and keep the knee rigid.  When the heel has been but slightly raised a sharp pain in the back of the thigh follows any effort to carry it higher.  Flexion of the leg to a right angle, increases the distance from the lines of insertion on the pelvic bones to the tuberosities of the tibia by two or three inches—­an amount of stretching these muscle cannot undergo.  Hence the knee must be flexed in flexion of the hip.

Experiment 30.  A similar experiment may be tried at the wrist.  Flex the wrist with the fingers extended, and again with the fingers in the fist.  The first movement can be carried to 90 degrees, the second only to 30 degrees, or in some persons up to 60 degrees.  Making a fist had already stretched the extensor muscles of the arm, and they can be stretched but little farther.  Hence, needless pain will be avoided by working a stiff wrist with the parts loose, or the fingers extended, and not with a clenched fist.

Review Analysis:  Important Muscles.

Location. 
Name.  Chief Function.

Head and Neck.

Occipito-frontalis. moves scalp and raises eye brow. 
Orbicularis palpebrarum. shuts the eyes. 
Levator palpebrarum. opens the eyes. 
Temporal. raise the lower jaw. 
Masseter. " " " "
Sterno-cleido-mastoid. depresses head upon neck and neck upon chest. 
Platysma myoides. depresses lower jaw and lower lip.

  Trunk.

Pectoralis major. draws arm across front of chest. 
Pectoralis minor. depresses point of shoulder,
Latissimus dorsi. draws arm downwards and backwards. 
Serratus magnus. assists in raising ribs. 
Trapezius.  Rhomboideus. backward movements of head and shoulder,
Intercostals. raise and depress the ribs. 
External oblique. various forward movements
Internal oblique. \ of trunk
Rectus abdominis. compresses abdominal viscera and acts upon

                                                      pelvis.