40 ELEMENTS OF MAMMALIAN ANATOMY. 



The articulation of a bone has reference to its contact 

 with other bones by means of joints. 



STRUCTURE OF BONE. 



Every bone is completely covered except on its articu- 

 lating surfaces with a tough membrane, the periosteum, 

 which serves for the attachment of muscles, and the 

 renewal of bony tissue in case of injury. The long bones 

 contain a cavity, the medullary cavity, filled with marrow 



FIG. 14. CROSS-SECTION OF CAT'S FEMUR. ( 5. 



cp, Compact tissue; en, cancellous tissue; en, endosteum; me, medullary 



canal; /><?, periosteum. 



(Fig. 12). This cavity is lined with endosteum, a mem- 

 brane similar to the periosteum. 



The shaft of the long bone is composed mainly of 

 compact bony tissue through which extend longitudin- 

 ally intercommunicating microscopic channels, Haversian 

 canals, for the conveyance of blood-vessels, nerves, and 

 lymphatics. 



The lacuna, or spaces for the bone cells during life, 

 are arranged concentrically about the Haversian canals. 

 The canaliculi, or processes of the lacunae, communicate 



