CH. V.] 



BONE 



lacunae take up the lymph exuded from the Haversian blood-vessels, 



and convey it to the substance of the bone which they traverse. 

 The blood-vessels enter the 



Haversian canals both from 



without, by traversing the small 



holes which exist on the surface 



of all bones beneath the perios- 

 teum, and from within by means' 



of small channels which extend 



from the medullary cavity, or 



from the cancellous tissue. The 



arteries and veins usually occupy 



separate canals, and the veins, 



which are the larger, often pre- 

 sent, at irregular intervals, small 



pouch- like dilatations. Nerve 



filaments are also found in the 



Haversian canals, and a little 



connective tissue with cleft-like 



lymph spaces. The larger canals 



may contain a few marrow cells. 

 The lacunae are occupied by 



branched cells, which are called 



lone-cells, or lone- corpuscles (fig. 



85); these closely resemble ordinary branched connective-tissue 



corpuscles. Bone is thus essentially connective tissue, the ground- 

 substance of which is impregnated 

 with lime salts. The bone-cor- 

 puscles with their processes, occu- 

 pying the lacunae and canaliculi, 

 correspond exactly to the connec- 

 tive-tissue corpuscles lying in 

 branched spaces. The connection 

 of the lacunae by the canaliculi 

 allows the nutrient lymph to pass 

 from place to place. 



Lamellae of Compact Bone. 

 In the shaft of a long bone three 

 distinct sets of lamellae can be 

 clearly recognised. 



1. Circumferential lamellae ; 

 these are concentrically arranged 

 just beneath the periosteum, and 



FIG. 85. Bone-corpuscies with their processes around the medullary cavity. 



as seen in a thin section of human bone. o rr i n 4-\^ 



(Boiiett.) 2. Haversian lamellae; these 



FIG. 84. Longitudinal section from the human ulna, 

 showing Haversian canals, lacunae, and canali- 

 culi. (Rollett.) 



