HISTOLOGY. 



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firm and consists of a peculiar substance called chondrin. When the 

 chondrin is nearly pure it is milky in appearance (hyaline cartilage, 

 fig. 15), but it may be invaded by numerous strands of fibrous or 

 elastic tissue, resulting in fibrous or elastic cartilage. Cartilage in- 

 creases in size by additions to the exterior and also by divisions of 

 its cells and by increase in the amount of matrix. Externally it is 



* 



FIG. 15. Hyaline cartilage. 



bounded by an envelope of connective tissue (perichondrium) which 

 bears blood-vessels and may give attachment to muscles, etc. 



Bone may arise directly from embryonic connective or fibrous tissue, 

 or by the ossification of cartilage. In either case the result is a strong 

 matrix composed of calcium phosphate and carbonate in a ground 



m 



FIG. 16. A, Stereogram of bone; B, cross-section of bone, more enlarged; c, canaliculi; 

 bl, bone lamellae; h, Haversian canal; /, lacuna. 



substance of organic matter (ossein). Minute tubes (Haversian 

 canals) , bearing blood-vessels, etc., run through the matrix (fig. 16), 

 and parallel to these canals or to the external surface of the bone are 

 the cells arranged in layers. The space occupied by a cell is called 

 a lacuna, from which minute tubules or canaliculi penetrate the matrix. 

 There are small spaces in many bones occupied by the red marrow, 



