The Skeletal System 95 



tion of parts of the ear, nose, and respiratory system. In the embryo, 

 this is the major type of cartilage present, and is the material in which 

 most of the bones are laid down. 



The matrix of this hyaline cartilage is a homogeneous semitrans- 

 parent material through which are spread numerous connective tissue 

 fibers. Widely scattered through the matrix are the rounded lacunae 

 containing the cells. 



Fibrous or zvhite cartilage is a modification of the hyaline cartilage 

 in which a large number of white fibrous connective tissue strands are 

 imbedded in the matrix. This tissue is found between the bodies of the 

 vertebrae and often in areas near joints. It is very strong and has 

 a degree of flexibility not found in bones. 



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ELASTIC 



Fig. 26. — Types of cartilage. 



Elastic or yellow cartilage has a matrix that contains many yellow 

 elastic connective tissue fibers. The presence of these fibers gives great 

 elasticity as well as a certain degree of strength to this issue. Elastic 

 cartilage is found in the external ear, in the epiglottis, and the cartilages 

 of the pharynx. 



Bone. — Bony tissue, in contrast to cartilaginous tissue, is a hard, 

 nontransparent, calcified material. Approximately two-thirds of its 

 weight is due to the presence of mineral salts. The remaining one-third 

 of the weight is due to the living cells, blood vessels, and other organic 

 materials. 



The microscopic structure of bone is best understood if first the 

 macroscopic details are considered. These latter are best seen by ex- 

 amining a longitudinal section (Fig. 27) of a bone such as one of the 

 long leg bones. The exterior portion of this bone is composed of heavy, 

 compact bone, while at both ends is a region composed of porous tissue 

 known as spongy bone. The shaft of the bone is hollowed out in the 

 center to form the marrow cavity. The marrow which fills this cavity 



