PASSIVE ORGANS OF LOCOMOTION. 



545 



canals being sometimes quite irregular. In the long bones their direction is generally lon- 

 gitudinal, although they anastomose by lateral branches. Each one of these canals con- 

 tains 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 arte- 

 ries penetrate and the veins emerge. Their size, of course, is variable. According to 

 Sappey, the largest are about -^5- and the smallest, -g^ of an inch in diameter. Their 

 average size is from -^ to ^^ of an inch. In a transverse section of a long bone, the 

 Haversian canals may be seen cut across and surrounded by from twelve to fifteen 

 lamella. In a longitudinal section the course and anastomoses may be studied. 



Lacunae. The fundamental substance is everywhere marked by irregular, micro- 

 scopic excavations, of a peculiar form, called lacunas or osteoplasts. These were at one 

 time supposed to be corpuscles of calcareous matter and were known as the bone-cor- 

 puscles ; but it has since been ascertained that this appearance is due to the imperfect 

 methods of preparation of the thin sections of bone. They are connected with numer- 

 ous little canals, giving them a stellate appearance. These are most numerous at the 

 sides. The lacunae measure from ^^ to -^^ of an inch in their long diameter, by about 

 s-^Vo of an inch in width. They contain the true bone-corpuscles, which we shall pres- 

 ently describe. 



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

 and presenting a communication between the first series of lacunae and the Haversian 



FIG. 161 Vascular canals and lacuna, seen in a transverse section of the humer-us; magnified 200 diameters. 



(Sappey.) 



1, 1, 1, section of the Haversian canals ; 2, section of a longitudinal canal divided at the point of its anastomosis with 

 a transverse canal. Around the canals, cut across perpendicularly, are Been the lacunas (with their canaliculi), 

 forming concentric rings. 



canals. Each osteoplast presents from eighteen to twenty canaliculi radiating from its 

 borders. Their length is from -^ to ^ of an inch, and their diameter, about 25 00 of 

 an inch. The arrangement of the Haversian canals, lacuna?, and canaliculi is shown in 

 Fig. 164. 



Bone-cells or Corpuscles. By treating perfectly fresh specimens of bone with weak 

 acid solutions, Virchow has demonstrated the presence of stellate cells or corpuscles, 

 exactly filling up the lacunae and sending prolongations into the canaliculi. These 

 structures have since been studied by Kouget, who has succeeded in demonstrating them 

 in fresh bones from the foetus, without using any reagent. They are stellate, granular, 

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

 35 



