102 



STRUCTURE OF THE VERTEBRATES 



cartilage, which is simplest and most abundant. In the discs be- 

 tween the vertebrae and other parts of the body the simple carti- 

 lage is strengthened by white connective tissue fibers, and is 

 known as fibrous cartilage. Elastic cartilage, containing elastic 

 fibers, is found in the larynx and other isolated parts of the 

 vertebrate. 



6. Bone is the hardest of the connective tissues. The bone 

 cells develop fibers which finely interlace, and then salts of cal- 

 cium and potassium are laid down in the spaces between the 

 fibers. So intimately are the organic and inorganic elements mixed 

 that either may be destroyed without affecting in the slightest 



Matrix 



Bone cells 



Hyaline cartilage 



Pcnosteiim 



' ,.y Haversian 

 system 





.M 



-f^-K" 



.45=. 





Bone section 

 (Low power) 



Fig. 43. Cartilage and Bone. 



Canaliculi^!^^A^W^^^'-q>. 



canal '^'s^^^---:.^.^-/ 'N 



Two Haversian Systems 

 (High power) 



the appearance of the minutest structure of the tissue. The cells 

 lie in spaces (lacunae) in the matrix, with microscopic canals 

 (canaliculi) radiating in all directions and joining the canals 

 from other cells. This r akes a protoplasmic connection through- 

 out the entire bone. The blood supply is secured from small 

 arteries and veins which pass longitudinally through the mat- 

 rix, a pair (artery and vein) lying in a Haversian canal. 



A cross section of a long bone shows that the matrix is laid 

 down as concentric layers or lamellae. The lamellae in contact 

 with the membrane surrounding the bone extend completely 

 around the shaft; but within these few concentric layers, the 

 lamellae surround the Haversian canals, forming Haversian sys- 

 tems. Each canal is surrounded by concentric lamellae, each 

 system being microscopic in size. The cell spaces lie between 

 the lamellae. A more complete discussion is given in Chapter 

 XI, page 172. 



Althou2;h the bones are structurallv similar, there are two de- 



