THE HUMAN STRUCTURE 



87: 



latter being powers. The bony substance is derived from an 

 elementary substance, plastic and gelatinous, which remains un- 

 altered in cartilages, ligaments, and tendons (71). When young, 

 the bones are in the cartilaginous state ; they gradually absorb 

 mineral salts (carbonate and limestone phosphates) and solidify. 

 The composition of bone is very variable ; from 16 to 68% of 

 water, and from 84 to 32% of solid matter, acccording to the 

 nature of the bone. In the solid part there is about 35% of 

 gelatinous organic substance : the " ossein " and 65% of lime- 

 stone salts ; these increase with age, whilst the amount of water 

 decreases ; in consequence,, the density of the bones changes 

 from 1'87 to 2 in the course of the first thirty years. 



The skeleton takes its formative elements from the alimenta- 

 tion, through the medium of the blood. 



The form of the bones vary, 

 those of the ocomotive limbs 

 being long and hollo'w tubes, 

 prismatic or practically cy- 

 lindrical enlarged at the ex- 

 tremities by which they are 

 connected or jointed. These 

 heads (epiphyses) are of a 

 spongy, lamellar substance, 

 the lamella being suitable 

 for sustaining pressure (figs. 

 94 and 95). They reveal, 

 as Culmann ( l ) showed, the 

 curve of pressures in the 

 arches. The mesial part (dia- 

 physis) is a compact tissue, 

 almost homogeneous and very 

 resistant. Besides long bones 

 there are flat bones, such as 

 the frontal bone, which have 

 lamellar matter between two 

 compact blades practically 

 parallel. 



There is also a large number 

 of bones of irregular shapes, 

 such as the bohes of the " ver- 

 tebral column/' and of the 

 foot and the hand. 



Fig. 95. Section of a femur 

 (thigh bone). 



Culmann Anwend d Graph Statik, vol. i. p. 128 (1888-1900; Zurich.) 



