66 ANATOMY FOR NURSES. [CHAP. VI. 



if the trunk and arms are the fixed point, the muscles draw the 

 pelvis upwards as a preparatory step to the elevation of the 

 lower limbs in the action of climbing. 



The diaphragm is a thin musculo-fibrous partition, placed 

 obliquely between the abdominal and thoracic cavities. It is 

 fan-shaped, and consists of muscle fibres arising from the whole 

 of the internal circumference of the thorax, and of an aponeu- 

 rotic tendon, shaped somewhat like a trefoil leaf, into which 

 the muscle fibres are inserted. (Vide Plate V, page 121, for 

 illustration of diaphragm.) It has three large openings for 

 the passage of the aorta, the large artery of the body, the in- 

 ferior vena cava, one of the largest veins of the body, and the 

 oesophagus or gullet ; it has also some smaller openings, of 

 less importance, for the passage of blood-vessels, nerves, etc. 

 The upper or thoracic surface of the diaphragm is highly 

 arched ; the heart is supported by the central tendinous por- 

 tion of the arch, the right and left lungs by the lateral portions, 

 the right portion of the arch being slightly higher on the right 

 than on the left side. The lower or under surface of the dia- 

 phragm is deeply concave, and covers the liver, stomach, pan- 

 creas, spleen, and kidneys. 



The action of the diaphragm modifies considerably the size 

 of the chest, and the position of the thoracic and abdominal 

 viscera, and it is essentially the great respiratory muscle of the 

 body. The mechanical act of respiration consists of two sets 

 of movements; viz. those of inspiration and of expiration, in 

 which air is successively drawn into the lungs and expelled 

 from them by the alternate increase and diminution of the 

 thoracic cavity. The changes in the capacity of the thorax are 

 effected by the expansion and contraction of its lateral walls, 

 called costal respiration, and by the depression and elevation 

 of the floor of the cavity, through contraction and relaxation 

 of the diaphragm, called diaphragmatic or abdominal respiration. 

 These two movements are normally combined in the act of 

 respiration, but in different circumstances one of them may be 

 employed more than the other. Abdominal respiration pre- 

 dominates in men and in children, and costal respiration in 

 women. 1 In the act of inspiration the diaphragm contracts, 



1 The costal respiration of women is abnormal, and has been shown to be 

 due to their mode of dress. 



