ANATOMY OF THE BONES. 481 



inch in thickness. 1 This matter is of an indefinitely and 

 faintly-striated appearance, but it cannot be reduced to dis- 

 tinct fibres. In the long bones the arrangement of the 

 lamellae is quite regular, surrounding the Haversian canals, 

 and forming what are sometimes called the Haversian rods, 

 following in their direction the length of the bone. In the 

 short, thick bones the lamellae are more irregular, frequently 

 radiating from the central portion to the periphery. These 

 peculiarities in the disposition of the fundamental substance 

 will be more readily understood after a description of the 

 Haversian canals. 



Haversian Canals. These canals exist in the compact 

 bony structure. They are absent, or very rare, in the spongy 

 and reticulated portions. Their form is rounded or ovoid, 

 the larger ones being sometimes quite irregular. In the 

 long bones their direction is generally longitudinal, although 

 they anastomose by lateral branches. Each one of these ca- 

 nals contains a blood-vessel, and their disposition constitutes 

 the vascular arrangement of the bones. They are all con- 

 nected with the opening on the surface of the bones, by 

 which the arteries penetrate and the veins emerge. Their 

 size, of course, is variable. According to Sappey, the largest 

 are about -fa and the smallest -g^-g- of an inch in diameter. 

 Their average size is from -^-g- to -g-J-g- of an inch. a In a 

 transverse section of a long bone the Haversian canals may 

 be seen cut across and surrounded by from twelve to fifteen 

 lamellae. In a longitudinal section the course and anasto- 

 moses may be studied. 



Lacunae. The fundamental substance is everywhere 

 marked by irregular, microscopic excavations, of a peculiar 

 form, called lacunae, or osteoplasts. These were at one time 

 supposed to be corpuscles of calcareous matter, and were 

 known as the bone-corpuscles ; but it has since been ascer- 

 tained that this appearance is due to the imperfect methods 



1 SAPPEY, Traite tfanatomie, Paris, 1866, tome i., p. 84. 



2 SAPPEY, op. cit., p. 76. 



31 



