The skeleton

The skeleton

These notes provide basic information on the skeleton which is intended to help you

understand the general osteology of the horse and dog. Much of this is also revision,

and more detailed information is provided where relevant, in subsequent chapters.

Introduction

The skeleton consists of the framework of hard structures which protect and support

its soft tissues. These include bones, cartilages and ligaments.

The skeleton can be divided into cranial (head) and post-cranial parts. The latter can

be divided into three parts:

(1) AXIAL SKELETON - the vertebral column, ribs and sternum.

(2) APPENDICULAR SKELETON - the bones of the limbs including the pelvic and

pectoral girdles

(3) SPLANCHNIC or VISCERAL SKELETON - bones developed within some soft

organs; e.g. os penis of the dog.

The number of bones in the skeleton varies with age (fusion in older animals) and

between individuals (e.g. caudal vertebrae and, in the horse, tarsus 6 or 7, carpus 7 or

8).

The bones can be roughly divided into four classes, depending on shape:

(1) LONG BONES - act as columns and levers in the limbs and consist of cylindrical

shafts (diaphyses) containing marrow and enlarged extremities (epiphyses). They

develop from at least three centres of ossification, one for the shaft (diaphysis)

and one for each extremity (epiphysis).

(2) FLAT BONES - provide protection for underlying organs (e.g. brain) and a large

area for muscle attachment (e.g. scapula).

(3) SHORT BONES - diffuse concussion (e.g. in the carpus and tarsus) or reduce

friction and modify the action of muscles and tendons (e.g. sesamoid bones

developed in some joints and tendons). They generally have only one centre of

ossification.

(4) IRREGULAR BONES - varied functions (include the median, unpaired bones of

the vertebrae and base of skull).