Muscles of the Horse and Their Purposes http://www.asaddlery.com/info/anatomy.htm#Muscles Muscles of the forehand Muscle/Ligament Origin Insertion Action Comment (where it point starts) (where it ends) Massester; cheek muscle Opens and closes the jaw. Allows chewing. Brachiocephalicus Wide Base of the Below the point of Moves the head from side Well developed for good strap like muscle skull behind shoulder to the to side, pulls the scapula movement. Too strong a the jaw humerus forward, raises it in rein contact stops free collection, swings the forward movement. foreleg forward. Sternocephalic Jowl Sternum Moves the head and neck. Over developed in ewe or bull necked horses, difficult to get into a relaxed shape. Rhomboideus Nuchal Scapula Lifts shoulder and the ligament forehand. Pulls the scapula forward. Splenius Behind the Beginning of the Turns and extends the Makes up the top line if poll Trapezius neck. well developed. Trapezius; flat sheet like Occipital Spines of the 7th Lifts shoulder and If this is well developed muscle . bone cervical and all the forehand the horse is working in a Thoracic vertebrae good outline. Nuchal ligament Poll Withers Helps muscles in the neck support the head Deltoid Scapula Humerus Flexes shoulder joint If over developed it will load the shoulder Supraspinatus Below the Point of shoulder Maintains the shoulder in Trapezius extension Latissimus dorsi Lower Back of the Flexes the shoulder and Thoracic humerus pulls the foreleg back. vertebrae Triceps Flexes the shoulder and extends the elbow Biceps Flexes the elbow and extends the shoulder Pectoral Helps pull the foreleg foreword. Triceps Brachii Extends the elbow joint Biceps Brachii Flexes the elbow joint Extensor Carpus Extend the knee Flexor Carpus Flexes the knee Digital Extensor Extends the toe and knee Digital flexor Flexes the toe and knee and extend the elbow. Muscles of the trunk, back, and ribs Muscles support the spine together with 3 ligaments and abdominal muscles. Muscle/Ligament Origin Insertion Action Comment (where it point starts) (where it ends) Spinalis Dorsi Beneath 4th cervical thoracic part vertebrae of Trapezius Lumbar muscles or Ilium Vertebrae along Extends the spine and Longest and strongest Longissimus dorsi the sine and the raises and supports the muscle, rider sits on them last 4 cervical head, neck . Main muscle vertebrae used in rearing, kicking, jumping and aids turning Intercostal muscles Spaces Aids breathing between ribs External and internal Attach to ribs Supports the internal abdominal oblique and pelvic organs bones Supraspinous ligament Poll Sacrum Supports head and neck, Spreads out, attaching to traction force aids support spines of the cervical in weak thoracic lumbar vertebrae, Called nuchal area. ligament in the withers and neck area. Muscles in the hindquarters Hindquarters are the engine of the horse, they should be well developed, strong to move the horse forward, particularly in the competition horse. Muscle/Ligament Origin Insertion Action Comment (where it starts) point (where it ends) Superficial gluteal Croup Bottom of the hip Flex and extend the More developed in a attached to the hip, pulls hind leg dressage horse. sacrum toward the body, used for rearing, galloping and kicking Biceps femoris Behind gluteals Bottom of the high Maintains hip joint in Main muscles over the attached to the extension hindquarters, part of the patella and tibia hamstring group, well developed in eventers, race horses. Semitendinosis Behind biceps Back of the Extends the hip and Part of the hamstring group, femoris hindquarters hock joints well developed in eventers and race horses. Semi membranosus Part of hamstring group, well developed in race horses /eventers. Gastrocnemius Rear of the femur Point of hock Maintains hip extension Peroneus tertius Femur Cannon bone With superficial digital muscle moves the stifle and hock. Achilles tendon Gastrocnemius Over point of hock Sacrosciatic ligament Sacrum and Pelvic bone coccygeal vertebrae .