48 ELEMENTARY HISTOLOGY. 



b. Articular cartilage. This forms caps covering the 

 ends of those bones which fit together to form move- 

 able joints : the caps act as elastic cushions to break 

 the force of shocks. 

 Mount in balsam a prepared section of articular cartilage from 

 the head of the femur, the section being made perpendicular to the 

 articular surface : examine ivith low and high powers. 



i. The matrix is hyaline or faintly granular. 



ii. The cartilage cells. Towards the free surface the 

 cells and cell groups become gradually flattened, 

 and arranged paralled to the surface. 



F. Bone. 



Bone consists of a dense fibrillar intercellular matrix, in 

 which are imbedded cells which lie in cavities connected with 

 one another by fine branching canals. The matrix is richly 

 impregnated with inorganic salts, chiefly phosphate and car- 

 bonate of lime, which form about two- thirds by weight of the 

 substance of the bone, and give it its great hardness and strength. 

 The matrix, with its contained bone-cells, is arranged in con- 

 centric layers or lamellse, around tubular passages, the Haversian 

 Canals, in which lie the bloodvessels, which penetrate the bone 

 in great numbers. A Haversian canal with its contained 

 bloodvessels, and its surrounding layers of matrix and cells, are 

 together spoken of as a Haversian system. 



1. Examine with both low arid high powers preimred trans- 

 verse sections of a long bone. 



i. The Haversian systems form the greater part of 

 the bone, and are readily recognised by the con- 

 centric arrangement of the lamellae, and the 

 central canals, 

 ii. The interstitial lamellae fill up the spaces between 

 the Haversian systems. They form parts of circles 

 which are in many cases of much larger radius 

 than the circles of the Haversian systems. 



iii. The lacunae are the spaces in the matrix in which 

 the bone-cells lie. In sections of dried bone the 

 lacuna) appear black, through being filled either 

 with air or with dirt. 



