THE SUPPORTING TISSUES 



39 



connective tissue cells and blood COlttDOSCd. of 

 vessels. ^ 



tough, as in the cartilages between the divisions of the 

 vertebral column. 



63. Osseous (Bony) Tissue. Just as ordinary connective 

 tissue supports and holds in place the delicate cells and 



fibers of the organs, so the bone 

 and cartilage support the various 

 complete organs and hold them in 

 their proper places in relation to 

 one another. Cartilage and bone 

 are closely related as to location 

 and function ; they are also closely 

 related in their development. For 

 FIG. 42. Ciliated Epithelial example, in infancy the flat bones 



Cells, which line the Air r . ,, r j -j r j_i_ 



Tubes. (Cilia are hairiike.) forming the roof and sides of the 

 a, large cells; b, young ceils;,, skull are soft and flexible, being 



cartilage, except a 

 patch of bone in the middle of each. 

 As growth proceeds, the bones touch and interlock, replac- 

 ing the cartilage. If a bone is broken, the new bone, as it 

 heals, is first cartilaginous and afterward solid. Late in life 

 some of the ordinary cartilages of the joints change to bone. 



64. Periosteum. A bone usually has its ends coated by 

 a layer of cartilage. At 



the margin of the sur- 

 face that forms the joint 

 the cartilage thins out, 

 and a layer of vascular 

 ("full of vessels'") con- 

 nective tissue begins 

 and, extending over the 

 remaining surface of 

 the bone, forms a cover- 

 ing for it, called the 

 periosteum. This con- 

 tains the blood vessels which pass into the bone to supply 



FIG. 43. Cartilage. A thin Section, highly 

 magnified. 



m, matrix ; a, group of two cartilage cells; b, a group 

 of four cells ; c , a cell ; , nucleus. 



