MINUTE ANATOMY OF BONE. 5 



longitudinal fibrous elements around the Haversian 

 canals. The secondary lamellae are the fibrous structures 

 disposed around the axis of the bone ; they are formed, 

 as the bone grows in thickness, by deposits beneath the 

 periosteum. Transverse fibres, known as the perforating 

 fibres of Sharpey, pass through the lamellae, pinning 

 them together. If a bone is carefully burned until all 

 the organic matter has been destroyed, it will, as in the 

 case of the macerated bone, retain its general form, even 

 to minute anatomical points, proving the uniform distri- 

 bution or diffusion of the earthy and animal matter 

 throughout the bone. A bone thus treated is brittle, 

 and readily crumbles under the weight of the hand. 



Filling the alveoli of spongy bone, and contained 

 within the medullary cavities of long bones, is a substance 

 known as marrow. It is of two kinds, the red and the 

 yellow. The former is found in all the bones in foetal 

 life and in the bones of the skeleton of the infant. In 

 the adult, all contain the red marrow except the long 

 bones, those provided with medullary cavities ; in these 

 the marrow is yellow and of the consistency of soft 

 cheese. Red marrow is a sticky fluid which contains 

 25 per cent, of solids, in which there is a trace of fat. 

 In it are found large multinucleated cells, giant cells, 

 supported by a delicate skeletal net-work of connective 

 tissue. Corpuscles resembling leucocytes are also ob- 

 served, as are also red blood-corpuscles. As red marrow 

 has been proven to be a blood organ, it is not extrava- 

 gant to assume that the changes in the corpuscular ele- 

 ments which have been described by some writers are in 

 reality the stages in the transformation of the white into 

 the red blood-corpuscles. The yellow marrow consists 

 almost entirely of fat, nearly 96 per cent., and subserves, 

 probably, the ordinary processes of nutrition. Bone is 



