HISTOLOGY 



27 



These fibrills are parallel to each other in tendons (C), which 

 have to convey strains in one direction; or they may be interlaced 

 confusedly, the tissue then forming sheets or membranes. Occasion- 

 ally, as between the skin and the muscles, the fibrous tissue may be 

 loose (areolar tissue). In elastic tissue fibres of another kind are 

 mingled among the non-elastic fibrils. These are yellow and elastic, 

 and when abundant give an elastic character to the whole. 



In cartilage and bone the matrix is more solid and is abundant. 

 These are the skeleton-building tissues. In cartilage the matrix is 

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



Fig. 17. — Connective tissues. A, embryonic, from Amhlystoma; B, expanded and 

 contracted pigment cells from Amblystoma; C, fibrous, from tendon. 



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

 fig. 18), 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 

 bounded by an envelope of connective tissue (perichondriuin) 

 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 substance of organic matter (ossein). Minute tubes (Hav- 

 ersian canals), bearing blood-vessels, etc., run through the matrix 

 Tig. 19), and parallel to these canals or to the external surface of the 



