ARTICULATION OF BONES 



The bones of the trunk assist to form a cavity, divisible into 

 three portions the thorax, the abdomen, and the pelvis. 



The bones of the four extremities contribute the solidity and 

 strength which are necessary for their uses in various positions of 

 the body. 



ARTICULATIONS (ARTHROSES) 



Articulations are formed when two or more bones are con- 

 nected together, or when bone and cartilage are joined. They 

 may be immovable or movable. 



IMMOVABLE JOINTS (SYNARTHROSES) 



In these the bones are held to- 

 gether firmly by fibrous tissue, some- 

 times by a thin layer of cartilage which 

 becomes calcified in later life. 



The best examples of immovable 

 joints are found in the skull, where 

 the flat bones are joined at their edges, 

 forming sutures. (See page 20, Fig. 12.) 



MOVABLE JOINTS (DIARTHROSES) 



In these the bones are not closely 

 joined, but are loosely connected by 

 ligaments which allow freedom of move- 

 ment between the surfaces. They are SHOWING 

 best studied in the extremities, where 

 all varieties of movable joints are 

 found. 



The essential structures in a movable joint are four in num- 

 ber: Articular bone, articular cartilage, ligaments, synovial mem- 

 brane -with synovia. 



The surfaces of bone which are to be connected together 

 (articular surfaces) are made of a specially hard compact tissue 

 called articular bone. It is smoother than other portions of the 

 bone and easily recognized by the eye. It has no periosteum, but 

 is covered by firm white hyaline cartilage the articular cartilage. 



1 1. ILLUSTRATION 

 ESSENTIAL STRUC- 

 IN A MOVABLE JOINT. 



(Diagrammatic.) 



