FUNCTION AND LOCATION OF THE MAIN MUSCLES, LIGAMENTS AND TENDONS IN THE HORSE’S BODY

Horses are kept because of their athletic ability; so the condition of the muscle is very important. Muscles are powerful and sensitive structures operating in particular groups or pairs, and can grow in size with appropriate work and nutrition, but the number of muscles in the horse’s body cannot be increased. Each muscle is attached to a stable part of the skeleton, and receives nerve messages, which when stimulated contract to moving another part of the skeleton. Muscles work in pairs, they can only contract or shorten, and it is the shortening of the opposite muscle that stretches the already contracted muscle.

Muscles Types

They are long and fibrous and arranged in bundles and bonded together by a membrane of fibrous connective tissue, they are about 60% water and therefore heavy. Muscle tissue can be separated into different types depending upon what is required of the muscle concerned: -

All types exist within the same muscle body and the relative proportions of each decide the performance type, i.e. sprinter, stayer or endurance horse.

Type of Muscle	Found	Description	Function
Cardiac	Highly specialised and is only found in the heart	Is striped with branching fibres Under a microscope it appears striped and has branching fibres that interconnect and allow the heart to act as a unit	Not under conscious control Enables the heart to work as a unit Has rapid powerful contractions and fibres which do not tire Cardiac muscle is capable of rapid changes of speed according to the body’s needs
Involuntary/Smooth/ Visceral	Lines the body cavities, blood vessels, digestive tract, the bladder and the uterus	Under the microscope it has no striations and the cells are spindle-shaped with a central nucleus	Not under conscious control Has a slower contraction time than skeletal muscle It can maintain rhythmic contractions for long periods, which allows peristaltic waves. (Bowel movement or swallowing)
Skeletal/Voluntary/ Striated	Throughout the body. About one third of the body weight	Appears striped when seen under a microscope and because it is under the horse’s control; he decides whether or not to twitch his ear or move his limbs	Moves the bones and is the muscle that we develop, while riding, schooling or when getting the horse fit to compete Supports the skeletal Structure Moves the skeleton through contraction of the muscle fibres Maintains joint stability, preventing undesirable, excessive movement Produces heat by shivering

Name	Location	Action	Comment
MASSETER	Cheek It is attached to a flat roughened area on the outer surface of the lower jaw. It is the main muscle of the horse’s cheeks	Closes the jaw and causes the grinding action for chewing	It is most important and powerful muscle used in mastication
BRACHIOCEPHALIC	Neck Attached to the wing of the atlas at the top of the horse’s neck just behind his ears, running down the length of the neck attaches to the humerus	Moves the head and neck to either side and brings the shoulder and forelimbs forward Lengthens the neck to extend or jump	Can be felt beneath the skin of the neck, forming the upper boundary of the jugular groove If the rider uses a restrictive rein contact, they will restrict the movement of this muscle
STERNO-THYRO-HYOIDEUS	Neck Runs down the underside of the neck on either side of the oesophagus and is a thin strap-like muscle	Assists in swallowing and sucking movements
RHOMBOIDEUS	Neck It stretches from the poll, runs under the trapezius muscle and attachs to the shoulder blade (Scapula)	Involved in lifting the shoulder and forehand	Ties the scapula into the trunk and the Ligamentum Nuchae The inner surface of the scapula provides attachment for the rhomboideus
STERNOCEPHALIC	Neck A long and narrow muscle, which extends from the angle of the jaw to the sternum and forms the lower border of the jugular furrow	Moves the head and neck	The jugular vein (common carotid artery), is subcutaneous (under the skin), and runs parallel to the sternocephalic
SPLENIUS	Neck Starts just behind the poll extending along the top of the neck to the trapezius	Acts to extend and turn the neck from side to side	When well developed, it helps to make up a good top line
TRAPEZIUS	Neck/Shoulder Lies on either side of the withers and over the rhomboideus and splenius muscles This flattened triangular sheet of superficial muscle, is attached to occipital bone at the top of the neck and at the bottom to the seventh cervical vertebrae and all of the thoracic vertebrae	Lifts the shoulder and forehand	In some horses these muscles are poorly developed which gives them prominent withers and ewe necks A well-developed trapezius is an indication that the horse works in a good outline
NUCHAL LIGAMENT	Neck/Shoulder The first part (funicular) is cord-like and passes forward from the backbone over the withers and attaches to the nuchal crest of the occipital bone The second part (lamellar) lies in the middle of the neck and forms fan-like branches, attaching at the top to the underside of the funicular portion and insert onto the middle five cervical vertebrae below	Assists the muscles of the neck in supporting the head
SUPERFICIAL PECTORAL and DEEP PECTORAL	Chest Starts from the sternum and costal cartilages The superficial pectoral passes outwards to attach to the shaft of the humerus and up around the front of the shoulder	To advance and adduct the leg	The deep pectoral pulls the leg back
SERRATUS VENTRALIS CERVICAL and SERRATUS VENTRALIS THORACIC	Chest The cervical part starts from the last five cervical vertebrae The two parts together form a fan-shaped muscle on the over the surface of the scapula	Supports the chest between the two shoulder blades	One other important factor concerning the ribs is that the first nine ribs are the start of the thoracic part of the serratus ventralis muscle
LATISSIMUS DORSI	Shoulder Attachs to the back of the humerus at the lower end and to the thoracic vertebrae	One of the main muscles used to flex the shoulder and leg
DELTOID	Shoulder The scapula spine is where the deltoid muscle starts and then crosses the outer surface of the shoulder joint to attach to the humerous	Flexes the shoulder joints and abduct legs
SUPRASPINATUS	Shoulder Below the trapezius to the point of the shoulder	Extends the shoulder joint	There is a bursa between muscle and shoulder joints
BICEPS BRACHII	Shoulder Starts from the lower end of the scapula	Extends the shoulder and flexes the elbow	There is a bursa present between tendon of biceps brachii and humerus bone
TRICEPS BRACHII	Chest Forms a bulge at the lower part of the shoulder, just above the elbow joint The humerus provides the attachment for the triceps	Help to flex the shoulder and extend the elbow joint	Comprise three separate muscles extending between the edge of the scapula and the point of the elbow Between them they make up the rounded muscle mass lying alongside the ribs just above the elbow The triangular section is the ‘bulge’ just in front of the saddle flap and underlies the rider’s knee
EXTENSOR CAPRI RADIALIS	Forearm	Extends the knee and flexes the elbow joints Attached to the extensor tendon, which run down the front of the cannon bone	The tendon possesses synovial sheath from approx. 10cm (4”) above to middle of knee
FLEXOR CAPRI RADIALIS	Forearm	Flexes the knee and extends the elbow joint	The muscle has a synovial sheath approx. 7cm (3”) above knee to that attaches to the cannon bone
Digital Extensor	Forearm	Extends the toe and knee	Become the tendons in the lower part of the limb
Digital Flexor	Forearm	Flexes the toe and knee and extends the elbow	Become the tendons in the lower part of the limb
EXTERNAL INTERCOSTALS and INTERNAL INTERCOSTALS	Abdomen Are respectively the superficial and deep muscles found between the ribs	The intercostals are responsible for part of the respiratory movement	Deeper muscles are also involved, in particular the muscular partition between the thoracic and abdominal cavities, the diaphragm
DIAPHRAGM	Abdomen A broad curved muscular partition between the chest and abdomen cavities attaching to the ribs, the cartilage of the sternum and the lumbar vertebrae	Can change the volume of the chest to help with breathing and can exert pressure on the abdomen during foaling	It forms a complete membrane except for three openings through which pass an artery (aorta), gullet (Oesophagus) and a vein (vena cava).
EXTERNAL ABDOMINAL OBLIQUE and INTERNAL ABDOMINAL OBLIQUE	Abdomen These muscles are attached to the ribs and to the dense tendonous sheet covering the loins and to the pelvis The whole abdominal wall is elastic and yields to finger pressure	Supports the weight of the internal organs and lifts the floor of the abdomen to help with functions such as urination, defecation, foaling, and exhaling	Internal muscles lie beneath the external ones These layers are important since they support the weight of the internal organs of the horse’s body The abdomen also mirrors the movements of the chest in respiration
LONGISSIMUS DORSI	Back Attached to the vertebrae Extending the back from the Spinalis Dorsi	Running along the back upon which the rider sits Of primary importance because it supports rider as well as transferring impulsion (energy) to the forehand from the hindquarters	The largest and longest muscle in the body These muscles along with associated ligaments support the skeleton and help maintain body shape
TENSOR FASCIAE LATAE	Pelvis	Flexes the hips and extends the stifle joint	Psoas minor is below the Longissimus Dorsi muscle and works in co-operation with the Longissimus Dorsi by contracting simultaneously in an effort to counter attempts to flex the spine
GLUTEAL	Hindquarters The bulk of the muscle that makes up the hindquarters and gives them their rounded appearance	They flex and extend the hip joint and abduct the leg. This is the main muscle concerned with the actions of rearing, kicking and galloping.	It has bursae (trochanteric) placed between tendon of muscle and the femur bone.
MAJOR TROCHANTER OF THE FEMUR	Hindquarters	The point of the hip, although it is deep it can be felt on the surface
BICEPS FEMORIS	Hindquarters Closely associated with the rear of the gluteal muscle; in fact, a slight groove may be felt between them It passes in a curved direction down the thigh covering the major trochanter, to the lateral surface of the leg where it is readily felt from the surface	Extends the limb as in rearing, kicking and galloping	There is a bursa between muscle and large trochanter and the back of the femur Part of the hamstring group
SEMITENDINOSUS	Hindquarters Extends along the rear border of the biceps femoris down the back of the thigh. The muscles end in a wide tendon on the inner surface of the stifle joint	Extends the hip and hock joints	Part of the hamstring group
LONG DIGITAL EXTENSOR	Gaskin or Second thigh Originates at the lower end of the femur. Its tendon passes over the front of the hock.	This muscle/tendon extends the toe and flexes the hock	Below the hock, this tendon is joined by the lateral digital extensor tendon, which attaches to the pedal bone.
LATERAL DIGITAL EXTENSOR	Gaskin or Second thigh Starts at the bottom of the femur and passes over the front of the hock, separated from the long digital extensor by a bursa	Below the hock it joints with the long digital extensor to form the extensor tendon that extends the toe and flexes the hock
PERONEUS TERTIUS	Gaskin or Second thigh Attaches to bottom of the femur, it then runs down the leg and just above the hock is divides into two halves; one branch attaches to the top of the cannon bone, and the other to the bottom bone of the hock joint (fourth tarsal bone).	Synchronises the action of the stifle and hock playing a purely mechanical role in the movement. It ensures that the hock flexes when the stifle flexes. It is for this reason that a horse with a straight stifle also has a straight hock and a horse with a bent stifle also has a bent hock	An entirely tendonous (cord-like) muscle that has an important bearing on the mechanism of the hock and stifle joints
GASTROCNEMIUS	Gaskin or Second thigh Extends from the rear of the femur, down the back of the Gaskin to the point of hock	Extends the hock and flexes the stifle joint There is a bursa between the tendon and the point of hock	Closely associated with the superficial digital flexor muscle, in maintaining the hock in extension About half way down the Gaskin the muscle turns into a tendon and along with the superficial flexor muscle, which is almost entirely tendonous, they form the Achilles tendon