34 



NORMAL HISTOLOGY. 



symphyses, the marginal plates and interarticular disks of certain joints, the 

 sesamoid cartilages and the lining of bony grooves for tendons. In its 

 physical properties, this tissue combines the flexibility and toughness of 

 fibrous tissue with the firmness and elasticity of cartilage. In structure, 

 fibrous cartilage resembles dense fibrous connective tissue, since the principal 

 constituents of its matrix are the wavy bundles of closely packed white fibres. 

 Between these bundles lie small irregularly distributed oval areas of hyaline 

 matrix (the so-called "capsules" ), which immediately surround the cartilage- 

 cells, singly or in groups. The number of cells and the proportion of fibrous 

 matrix differ in various localities. A distinct perichondrium is wanting. 



BONE. 



Bone or osseous tissue is a dense form of connective tissue, the matrix 

 of which is impregnated with lime-salts; to this modification, shared by the 

 dentine of the teeth, is due the characteristic hardness of the tissue. In 



FIG. 48. Section of frontal bone, showing the spongy bone enclosed within the lamellated compact bone ; 

 the latter, however, does not contain Haversian systems. X 18. 



the higher animals, osseous tissue supplies the supporting framework, or 

 endoskeleton; among certain lower vertebrates there exists an exoskeleton as- 

 sociated with the integument and composed of protecting masses of horny 

 substance, represented by the dermal plates of .the crocodile or the shell of 

 the turtle. Within various organs, as the sclerotic coat of the eye of birds, 

 the diaphragm of the camel, the tongue of some birds or the snout of the 

 hog, bone constitutes the splanchnoskeleton. True osseous tissue does not 

 occur outside the vertebrates, the skeletal frameworks of invertebrate ani- 

 mals consisting of calcareous incrustations or of silicious structures. 



