398 MOVEMENTS OF RESPIRATION. [CHAP. XXIX. 



observations ; whereas in women, this movement is very obvious, 

 particularly in the upper ribs. It is not improbable that the cause 

 of this may lie in the narrower waist of the female, obliging an 

 undue enlargement of the upper part of the thorax to compensate 

 for the smaller size and less dilatability of the ample base. The 

 separation of the ribs and widening of the intercostal spaces when 

 the chest is enlarged, are proved by measurement both in the living 

 and dead. Dr. Hutchinson has made casts of the interior under 

 both states. Dr. Sibson divides the ribs into three sets, a superior 

 set of five separately joining the sternum, an intermediate set of 

 three, with conjoint cartilages, and an inferior or diaphragmatic 

 set of four with floating cartilages. He considers that all, except 

 the upper four in their front part, diverge from one another in 

 inspiration, the inferior set the most, but the lowest of all remain- 

 ing stationary. Messrs. Beau and Maissiat* describe three varieties 

 of ordinary respiration : 1. Abdominal, or that chiefly effected by 

 the diaphragm, and apparent in the motion of the abdominal walls. 

 This occurs in infants up to the end of the third year, and in males 

 generally. 2. Costo-inferior, or that in which the lower ribs (those 

 of Dr. Sibson' s intermediate and inferior sets) are observed to act. 

 This is observed in boys after three, and in men. 3. Costo- superior, 

 or that effected in a considerable degree by the upper ribs. This 

 is observed in females, especially in adults. 



Action of Muscles. The diaphragm has an arched form, is 

 highest in front, lowest behind. The fibres pass to a central tendon 

 on which is seated the heart in the pericardium, the lungs resting 

 chiefly on the muscular parts. Its contraction would tighten and 

 then depress both the central tendon and the muscles generally, and 

 would also tend to straighten the curves formed by the fibres as 

 they pass from the spine and ribs to the central tendon. Thus the 

 heart would be lowered a little, but, perhaps the lungs more, and 

 the area of the pulmonary compartments of the thorax would be 

 much enlarged, for the diaphragm acts on their wide and ample 

 base, where a slight range of vertical movement produces a great 

 effect. In its descent the diaphragm presses down the abdominal 

 viscera, and bulges the abdominal walls. In expiration it recedes 

 upwards, being pushed upon by the abdominal walls through the 

 medium of the viscera. 



The action of the intercostal muscles is less obvious, and had been 



the subject of much difference of opinion, even before the days of 



Haller. It may be studied on mechanical principles, and by obser- 



* Archiv. Gen. de Med. t. xv. p. 399. 



