32 PRINCIPLES OF VETERINARY SCIENCE 



(a) Compact bony tissue is dense, close grained, and varies in 

 thickness. In long bones it occurs in greatest amount in the 

 shaft, the center of which is almost exclusively composed of it. 

 Toward the ends of long bones it gradually diminishes in thickness 

 until at the extremities it forms only a shell-like covering. On 

 account of its resistance it is found in abundance wherever great 

 strain is placed on a bone. In the cannon bone it is thick in the 

 center, but thicker in front than behind, and on the inside than 

 outside, in correspondence with the lines along which the great- 

 est weight of the body falls. 



A close examination of the structure of the compact tissue 

 shows a series of extremely thin plates or bars of bony substance 



Fie. 4. — Transverse section from the shaft of a long bone, showing microscopic 

 appearance of compact bone tissue. (Bohm and Davidoff.) 



that are generally arranged in rings around small channels, 

 known as Haversian canals, in which blood-vessels pass in the 

 direction of the long axis of the bone (Fig. 4). Between these 

 plates are spaces called lacunae that communicate with each 

 other and with the Haversian canal by means of numerous ex- 

 tremely small canals or canaliculi. Through these connecting 

 channels nutrient fluids find their way to all parts of the bone. 

 (b) Cancellated bony tissue is porous in appearance and com- 

 posed of great numbers of little bonyplates and spicules surround- 

 ing spaces that are filled with red marrow in the living animal. 

 There is little spongy tissue in the centers of the shafts of long 

 bones, but at the extremities it increases in amount and forms 

 nearly the entire mass. It is less resistant than compact bony 

 tissue, but is useful in giving the bones surface without adding 



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