178 HEALTH AND DISEASE 



To whatever class a bone may belong it will have upon it eminences and 

 depressions. Some of these will be articular, and by uniting with other 

 bones form joints, while others will be non-articular, and give attachment 

 or lodgment to ligaments, muscles, or tendons. 



GROWTH OF BONES 



In the course of the growth of the foetus much of the skeleton is laid 

 down in a soft flexible substance termed cartilage or gristle, out of which 

 bone is ultimately developed by a succession of changes, including the 

 deposition of mineral matter into its structure. In long bones this process 

 of ossification is first commenced in the centre of the diaphysis or shaft, 

 from which it spreads to the extremities, where it is ultimately met by an 

 ossifying centre from each. The two ends are termed epiphyses, and 

 during the period when the animal is growing they may be, and sometimes 

 are, broken away from the shaft by muscular contraction and other forms 

 of violence. Where a considerable projection appears on a bone, as on 

 the upper end of the femur, they are produced from separate centres of 

 ossification and known as apophyses. 



Growth in length takes place between the ossifying centre in the shaft 

 and those of the extremities; in thickness it proceeds from the inner surface 

 of the periosteum, which lays down bony matter layer upon layer. 



Flat bones, such as those which enter into the formation of the cranium, 

 the scapula or blade bone, &c., are developed between two membranes and 

 not, as in long bones, from a pre-existing model of cartilage. The former 

 is termed intra-membranous- ossification, the latter intra-cartilaginoux. 



SKELETON 



The skeleton is the bony framework which gives attachment to muscles, 

 forms cavities for the safe lodgment of the organs essential to life, and gives 

 general support to the body. When the bones are united by their proper 

 ligaments the skeleton is said to be a natural one, but when they are 

 held together by wire, catgut, and other foreign materials, it is termed an 

 artificial skeleton. 



The skeleton of the horse is made up of about 163 bones, which are 

 united in various ways to form joints movable or fixed, according to the 

 purpose of the part into which they enter. 



The skeleton is divided into trunk and extremities. The trunk com- 

 prises the head and spinal column, the ribs, the sternum, and pelvis. The 

 extremities are distinguished as the fore and hind, or the thoracic and pelvic. 



