PASSIVE ORGANS OF LOCOMOTION 



429 



phate, sodium phosphate and sodium chloride. The relative propor- 

 tions of the organic and inorganic constituents are somewhat variable ; 

 but the average is about one-third of the former to two-thirds of salts. 

 This proportion is necessary to the proper consistence and toughness of 

 the bones. 



Anatomically, the fundamental substance of the bones is arranged 

 in the form of regular concentric lamellae, about ^V^ of an inch (8 p ) in 

 thickness. This matter is of an indefinitely and faintly striated appear- 

 ance, but it can not be reduced to distinct 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, fre- 

 quently radiating from the central 

 portion toward the periphery. 



The Haversian canals are found 

 in the compact bony structure. 

 They are either absent or 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 

 usually is longitudinal, although 

 they often anastomose by lateral 

 branches. Each one of these 

 canals contains a bloodvessel, and their disposition constitutes the 

 vascular arrangement of the bones. They are all connected with open- 

 ings on the surfaces of the bones, by which the arteries penetrate and 

 the veins emerge. Their size, of course, is variable. The largest are 

 about g 1 ^ of an inch (400 /-t) and the smallest -g J^ of an inch (30 /JL) 

 in diameter. Their average size is ^i^ to 2ZT f an inch(ioo 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. 



Lacunce. The fundamental substance is everywhere marked by 

 irregular microscopic excavations, of a peculiar form, called lacunae. 

 They are connected with little canals, giving them a stellate appearance. 

 These canals are most abundant at the sides of the lacunae. The 



Fig. 87. Vascular canals and lacunce seen in a lon- 

 gitudinal section of the hurnerus, x 200 (Sappey). 



a, a, a, vascular canals; b, b, b, lacunas and can- 

 aliculi in the fundamental substance. 



