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The Basis of the Skeletal System
The basis of support and movement of the horse is made possible by the combined effort of the skeletal and muscular systems. In this article we will look closely at what constitutes the skeletal system.

The skeletal system includes all bones attached at joints, cartilage between the joints & fibrous ligaments. The system has several roles in the physiology of the horse, these are -
support of the soft tissues, providing the framework of the horse's body
protection of delicate internal organs

leverage - providing attachment for ligaments, muscles and tendons
mineral storage - especially calcium and phosphorus
blood cell production takes place in the marrow of many long bones


A bone is a living tissue with nerves and blood vessels.  It contains proteins and minerals, particularly calcium and phosphorus.  To achieve and maintain a healthy skeleton the horse must receive adequate amounts of these minerals.

Bone consists of the hard outer cortex, encasing an inner area of spongy bone, called the medullary cavity.  Within this cavity is the marrow, where new blood cells are made. The entire surface of the bone is covered by a thin membrane called the periosteum.

On the basis of shape, bones are classified as either -
long bones such as the cannon or radius
short bones such as the carpal and tarsal bones
flat bones such as the scapula
irregular bones such as the vertebrae

A joint (or articulation) is a point of contact between bones or between cartilage and bones. Joints allow movement. They may be classified into the following types - 
fibrous joints - bones held by fibrous connective tissue, with no joint cavity (e.g. the skull). Allow little or no movement.

(Left - synovial joint)
cartilaginous joints - bones held by cartilage, with no joint cavity (e.g. the vertebrae). The articulating bones are held together tightly, allowing little movement.
synovial joints - contain a joint (synovial) cavity, articular cartilage and a synovial membrane (e.g. the fetlock).  A fully moveable joint.


Cartilage
is a gristly connective tissue containing collagen and elastic fibres  covering the ends of bones at some joints. It contains no blood vessels or nerves.

A ligament is a dense fibrous tissue that connects bone to bone.  Horses also have "check ligaments" which connect some bones & tendons and form part of the horse's "stay mechanism". They lock the limbs and joints so that the horse can relax and sleep in a standing position.

Tendons
connect muscle to bone and help control the movement of bones and joints. In the horse there are no muscles below the knee or hock. All movement of the pastern and foot is transferred by tendons connected to muscles in the upper limbs.

Both tendons and ligaments have a poor blood supply, making healing difficult following injury. 


The skeletal system consists of approximately 205 bones divided into -
the axial skeleton includes all but the limbs - the skull, vertebrae, sternum and ribs and the appendicular skeleton - including the four limbs of the horse.  There is variation in the number of bones, as some fuse together as the horse matures. Even in adult horses there can be variation in the number of bones. E.g. anything from 15 to 21 coccygeal or caudal (tail) vertebrae


Cyberhorse 2004 Melissa Alexander

 

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