PHYSIOLOGICAL ANATOMY QF THE BONES. 



483 



The Haversian canals exist in the compact bony structure. They are 

 either absent or are very few in the spongy and reticulated portions. Their 

 form is rounded or ovoid, the larger canals being sometimes quite irregular. 

 In the long bones their direction is generally longitudinal, although they 

 anastomose by lateral branches. Each one of these canals contains a blood- 

 vessel, and their disposition constitutes the vascular arrangement of the 

 bones. They are all connected with the openings on the surface of the 

 bones, by which the arteries penetrate and the veins emerge. Their size, 

 of course, is variable. The largest are about -fa of an inch (400 //,) and the 

 smallest, -^ of an inch (30 /x) in diameter (Sappey). Their average size 

 is -pfa to fg- of an inch (100 to 125 //,). In a transverse section of a long 

 bone, the Haversian canals may be seen cut across and surrounded by twelve 

 to fifteen lamellae. 



Lacuna. The fundamental substance is everywhere marked by irregular, 

 microscopic excavations, of a peculiar form, called lacunae. They are con- 

 nected with little canals, giving them a stellate appearance. These canals 

 are most abundant at the sides of the lacunae. The lacunae measure y^^ to 

 -5^-5- of an inch (20 to 30 /x) in their long diameter, by about --$-$ of an inch 

 (10 /*) in width. 



Canaliculi. These are little, wavy canals, connecting the lacunae with 

 each other and presenting a communication between the first series of lacunas 

 and the Haversi- 

 an canals. Each 

 lacuna presents 

 eighteen to twen- 

 ty canaliculi radi- 

 ating from its 

 borders. The 

 length of the can- 

 aliculi is -gfo to 

 -inhr of an inch 

 (30 to 40 /x), and 

 their diameter is 

 about ^^ of an 

 inch (1 //,). The 

 arrangement and 

 relations of the 

 Haversian canals, 

 lacunae and cana- 

 liculi are shown 

 in Fig. 160. 



Bone-cells or Corpuscles. These structures are stellate, granular, with a 

 large nucleus and several nucleoli, and are of exactly the size and form of 

 the lacunae. They send out prolongations into the canaliculi, but it has 

 been impossible to ascertain positively whether or not they form membranes 

 lining the canaliculi throughout their entire length. 



FIG. 160. Vascular canals and lacunce. seen in a transverse section of the 

 humerus ; magnified 200 diameters (Sappey). 



1,1,1, section of the Haversian canals ; 2, section of a longitudinal canal di- 

 vided at the point of its anastomosis with a transverse canal. Around the 

 canals, cut across perpendicularly, are seen the lacunae (with their canali- 

 culi), forming concentric rings. 



