BONE 



41 



Elastic and White Fibro-Cartilage. The first variety is found* in 

 the cartilage of the external ear; the latter in portions of the joints, the inter- 

 vertebral cartilages, etc. 



Structure. Elastic and white fibro-cartilage are composed of cells and a 

 matrix; the latter being made up almost entirely of fibers closely resembling 

 those of fibrous connective tissue. 



Development of Cartilage. Cartilage is developed out of mesoblast cells 

 with a very small quantity of intercellular substance. The cells multiply by 

 fission within the cell-capsules. 



BONE. 



The characteristic of bone is that the matrix is solidified by a deposit of 

 earthy salts, chiefly calcium phosphate, but some magnesium phosphate and 

 calcium carbonate. 



To the naked eye there appear two plans of structure in different bones, 

 and in different parts of the same bone, namely, the dense or compact, and 

 the spongy or cancellous tissue. In a longitudinal section of a long bone, 

 as the humerus, the articular extremities are found capped on their surface 

 by a thin shell of compact bone, while their interior is made up of the spongy 

 or cancellous tissue. The shajt is formed almost entirely of a thick layer 

 of the compact bone which surrounds a central canal, the medullary cavity, 

 so called from its containing the medulla, or marrow. In the flat bones, the 

 parietal bone or the scapula, a layer of cancellous structure lies between 

 two layers of the compact tissue. In the short and irregular bones, as those 

 of the carpus and tarsus, the cancellous tissue alone fills the interior, while 

 a thin shell of compact bone forms the outside. 



The Marrow. There are two distinct varieties of marrow the 

 red and the yellow. 



FIG. 52. Cells of the Red Marrow of the Guinea- Pig. highly magnified, a, A large cell, the 

 nucleus of which appears to be partly divided into three by constrictions; b, a cell, the nucleus of 

 which shows an appearance of being constricted into a number of smaller nuclei; c, a so-called 

 giant cell, or myeloplaxe, with many nuclei; d, a smaller myeloplaxe. with three nuclei; e-i, proper 

 cells of the marrow. (Schafer.) 



