HISTOLOGY. 23 
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 
Fic. 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 
Fic. 16.—A, Stereogram of bone; B, cross-section of bone, more enlarged; ¢, canaliculi; 
bl, bone lamelle; 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, 
