CH. V.] 



BONE 



43 



other canals but these may be visible ; but on making a transverse 

 section of the compact tissue as of a long bone, e.g., the humerus or 

 ulna, the arrangement shown in fig. 55 can be seen. 



The bone is mapped out into small circular districts, at or about 

 the centre of each of which is a hole, around which is an appearance 

 as of concentric layers; the lacunce and canaliculi follow the same 

 concentric plan of distribution around the small hole in the centre, 

 with which indeed they communicate. 



On making a longitudinal section, the central holes are found to 

 be simply the cut extremities of small canals which run lengthwise 

 through the bone, anastomosing with each other by lateral branches 

 (fig. 56); these canals are called Haversian canals, after the name 



FIG. 56. Longitudinal section from the human ulna, 

 showing Haversian canals, lacunae, and canali- 

 culi. (Rollett.) 



FIG. 57. Bone-corpuscles with their processes 

 as seen in a thin section of human bone. 

 (Eollett.) 



of the physician, Clopton Havers, who first accurately described 

 them. They are occupied by blood-vessels. 



The lacunae are occupied by branched cells, which are called 

 lone-cells, or lone- corpuscles (fig. 57) ; these closely resemble ordinary 

 branched connective- tissue corpuscles. Bone is thus essentially con- 

 nective tissue, the ground-substance of which is impregnated with 

 lime salts. The bone-corpuscles with their processes, occupying the 

 lacunae and canaliculi, correspond exactly to the connective- tissue 

 corpuscles lying in branched spaces. The connection of the lacunae by 

 the canaliculi allows the nutrient lymph to pass from place to place, 



