SPECIAL PHYSIOLOGY OF MUSCLES. 67 



very numerous. Their action is to impart to the forearm and hand a 

 variety of movements, such as pronation, supination, flexion, ex- 

 tension, rotation, etc. 



The pectoralis major and pectoralis minor muscles form the fleshy 

 masses of the breast. Arising from the inner half of the clavicle, the 

 side of the sternum, and the outer surfaces of the third, fourth, and 

 fifth ribs anteriorly, the muscle-fibers converge to be inserted into 

 the humerus and coracoid process. Their combined action is to 

 adduct, flex and rotate the arm inward, and to draw the scapula down- 

 ward and forward, movements necessary to the folding of the arms 

 across the chest. 



The rectus abdominis and the obliquus externus assist in forming 

 the abdominal walls. 



The glutei muscles are three in number, are arranged in layers, and 

 form the fleshy masses known as the buttocks. They arise from the 

 side of the pelvis and are attached to the femur in the neighborhood 

 of the great trochanter. Their action is to extend the hips, to raise 

 the body from the stooping position, and to assist in walking by 

 firmly holding the pelvis on the thigh while the opposite leg is ad- 

 vanced in the forward direction. 



The rectus femoris, with its associates, the rectus internus and 

 rectus externus and the crureus, forms the fleshy mass on the an- 

 terior surface of the thigh. The former arises from the anterior 

 part of the ilium, the latter from the femur. Their common tendon, 

 which is united to the patella, is continued as the ligamentum patellae, 

 which is attached to the upper part of the tibia. The action of this 

 muscular group is to extend the leg, to flex the thigh, and to raise 

 the entire weight of the body, as in changing from the sitting to the 

 erect position. 



The biceps femoris muscle, situated on the outer and posterior 

 aspect of the thigh, arises from the tuber ischii, and is inserted into 

 the head of the fibula. 



The semimembranosus and the semitendinosus muscles, -situated 

 on the inner and posterior aspect of the thigh, are inserted into the 

 head of the tibia. Their combined action is to extend the hips and 

 to flex the knee. Acting from below, they assist in raising the 

 body from the stooping position. 



The gastrocnemius muscle forms the enlargement known as the 

 calf of the leg. It arises by two heads from the condyles of the 

 femur. Its tendon, the tendo Achillis, is inserted into the posterior 



