20 



OSTEOLOGY 



STRUCTURE OF BONES' 



Bones consist chiefly of bone tissue, but considered as organs they present 

 also an enveloping membrane, termed the periosteum, the medulla or marrow, 

 vessels, and nerves. 



The architecture of bone can be studied best by means of longitudinal and 

 cross-sections. These show that the bone consists of an external shell of dense 

 compact substance, within which is the more loosely arranged spongy substance. 



Fig. 1. — Frontal Skction of Large Metatarsal Fig. 2. — Sagittal Section of Large Metatarsal 



Bone of Horse, Posterior Part. Bone of Horse. 



iS'.C, Compact substance; S.s., spongy substance; Cm., medullary cavity; F.n., nutrient foramen. Note the 

 greater thickness of the compact substance of the inner and anterior parts of the shaft. 



In typical long bones the shaft is hollowed to form the medullary cavity (Cavum 

 medullare). 



The compact substance (Substantia compacta) differs greatly in thickness in 

 various situations, in conformity with the stresses and strains to which the bone is 

 subjected. In the long bones it is thickest in the middle part of the shaft and thins 

 out toward the extremities. On the latter the layer is very thin, and is especially 

 dense and smooth on joint surfaces. 



' Only tho fi;ross structure is discussed here, 

 be made to iiistological works. 



For the microscopic structure reference is to 



