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138 thorax, which are pressed downwards by the droop­ing of the ribs.

Now in respiration a constant alternate motion takes place between the chest and abdominal cavity, which we may as well explain here, as many ladies think that so long as the chest remains free from pressure the abdomen may be tightened without danger or inconvenience. The division between the chest and abdomen is formed by a strong muscle called the diaphragm or midriff, which is nearly circular in form, and is attached in front, under the cartilages of the breast-bone along the sides, to the cartilages of the six lower ribs, whilst at the back it is firmly fixed to the first lumbar vertebra. It occupies an oblique position in the centre of the body, rising into the thoracic cavity during expira­tion; and as we inspire it is pressed downward into the abdominal cavity, materially assisting di­gestion by its action. Of course, as the diaphragm descends the capacity of the chest becomes enlarged to a considerable extent, while at the same time the abdomen is pushed outwards to make room for the inflation of the lungs. The intercostal muscles, or those between the ribs, also exert a very considerable influence in raising the ribs during inspiration, and thus increasing the size of the