SECOND LECTURE. 



BONES. 



44. THE study of Bones is termed Osteology. Before entering, 

 however into the details of the diseases and accidents pecuUar to the 

 bones of domestic animals, I will first briefly run over the general 

 skeleton. 



45. What is Bone ? It is a yellowish-white, hard, ordinarily 

 insensitive substance, made up of two tissues, one of which is 

 hard or compact, the other being porous or cancellated ; while it is 

 composed of one-third animal and two-thirds earthy matter, and is 

 covered by a tough membrane called pei'iosteum, and lined internally 

 with a fine membrane called endosteum. Bone is the basis of the 

 animal frame or skeleton — giving attachment to the soft parts, and 

 shielding the delicate organs. For descriptive purposes bones are 

 divided into three classes, as long, flat, short and irregular. 



46. Periosteum, or the outer covering of bone is a dense fibro- 

 vascular membrane, consisting of two layers, an outer fibrous one, and 

 an inner one of fine connective tissue which is contituied into the 

 Heversian Canals, by which means the bone is nourished. The 

 periosteum varies in thickness according to the position of the bone, 

 being thickest where the bone is most exposed to injury, for instance, 

 on the Tibia and Shank Bone. 



47. Endosteum is a very fine vascular membrane, lining the 

 internal or medullary cavities of the bones, wherein the marrow (a 

 fatty substance) is contained, and by its means the internal arteries 



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