6o 



ELEMENTARY PHYSIOLOGY 



(intercostal muscles) which unite them. These, together with the back-bone 

 behind, and the breast-bone in front, form the walls of the upper portion of 

 the great cavity. The lower portion has no such firm framework. It is 

 supported by the vertebral column behind ; but, round the sides and front, 

 the walls consist of flesh and fibrous connective tissue only. The flesh consti- 

 tutes the muscles of the abdomen, abdomen being the name of the lower 

 portion of the great body cavity. 



Fig. 73. The Cavities of the 

 Human Body. 



i, bodies of the vertebrae ; 2, spinous 

 processes of the vertebrae : 3, spinal 

 canal ; 4, breast-bone ; 5, diaphragm ; 

 6, thorax ; 7, abdomen. 



Fig. 74. The Diaphragm, &c. 



a, sixth dorsal vertebra ; b, fourth lumbar vertebra ; 

 c, lower cartilaginous extremity of the breast-bone 

 (ensiform cartilage) ; dd ' } a great blood-vessel (aorta) 

 passing through the diaphragm ; e, oesophagus ; 

 j, opening through which a great vein (inferior vena 

 cava) passes ; i, 2, and 3, tendinous portion of the 

 diaphragm ; 4 and 5, muscular portion of the dia- 

 phragm ; 6 and 7, the pillars of the diaphragm. 

 These are pow erful muscles which connect the ten- 

 dinous portion of the diaphragm with the spinal 

 column. 8, 9, and 10, intercostal muscles. 



Now insert the point of a knife just at the lower extremity of the sternum, 

 and cut through that bone toward the throat, thrusting the knife no deeper 

 than is absolutely necessary. The front walls of the cavity, consisting of the 

 ribs and the intercostal muscles, may now be carefully cut away, so as to ex- 

 pose the interior. If we now carefully remove the organs which are contained 

 in this portion of the body cavity (the heart and the lungs) we shall find that 



