So much is the abdomen drawn in wards by deep inspiration, that the portion of the continuous line (figs. 711, and 712.), representing the ordinary breathing is (over the abdominal region) external to the dotted line of deep inspiration. Therefore the greatest enlargement of the thoracic cavity in both sexes is made by the ribs, and not by the diaphragm, as is generally believed. It appears very questionable whether the dia phragm is any thing more than flattened and that without descending.
Of the position of the diaphragm. — It is clear that all that space between the line of ordinary breathing and deep inspiration (fig. 711.), below the ensiform cartilage, where the two lines cut each other, may be considered as just so much space deducted from the abdominal cavity ; and therefore the abdominal cavity, by deep breathing, is just so much less than it was in the posi tion of ordinary breathing. Now, if the dia phragm descends at this moment, whilst the abdominal parietes are being constringed on all sides, what becomes of the abdominal vis cera? We know that in ordinary breathing the abdomen advances because the diaphragm descends, and recedes because the diaphragm ascends. We may suppose the same accom modating movement between the diaphragm and abdominal parietes, to take place in deep breathing. There can be no doubt that the cir cumference of the thorax is increased, as shown in n.fig. 670., and that the diaphragm must extend its borders, and consequently the arch must be flattened ; but this may be without descending. We see (fig. 670.) that the sec tion of the thorax to the area of the diaphragm is as 40 to 133—the concavity of the dia phragm is enough to admit of its circumfe rence expanding without its descending.
Fig. 715. is a diagram of sections of the base of the living chest in three stages. B is the chest in ordinary : A, as in extreme expiration ; c, as in extreme inspiration. In this case the vital ca pacity was 305 cubic inches, and the mobility of the chest was 5 inches, a range by no means common. The area of the chest varied 27 superficial inches between extreme inspiration and expiration.* In the sitting posture the same relations exist in the breathing movements ; the only difference being that these movements are more limited.
- (c) Of the deep expiratory position. — In figs. 711. and 712. the margin of the shade is the position of the thoracic boundaries in deep expiration.
We have supposed the figures above merf tioned as standing with the back fixed, for the purpose of making clearly manifest the relative position of these several breathing movements. In fig. 716. the body is quite free, and wholly alters its position in performing expiration and inspiration. This should al
-ways be considered in noticing the breathing movements in diagnosis.
(d) Of the change of position by extreme breathing. — In expiration the head is pro truded and lowered (see figs. 713. and 714.). Therefore, by inspiration the body is raised, and the more erect the more can be inspired ; by expiration it is lowered, so much so that we have seen men when displacing their vital capacity volume stoop themselves to one-half their natural height, to one-sixth frequently: we speak from a large number of cases,— nearly 4000. Physiologists have reasoned that, as upon the principle of a bladder becom ing longer when empty than when inflated, so the chest is shorter when inflated than when empty. But this example in no way corresponds. The bladder expands, because it is inflated ; the chest is inflated because it expands.
We have given the position of the breath ing parts (the body fixed) : we shall describe the movement of these parts relatively in time and order to each other, and the peculiar character of these movements in health, and some of their modifications by disease.
Ordinary breathing.—In men this is sym metrical, and very limited, and commences with an advancing and receding of the abdo men at and above the umbilical region, accom panied with a slight lateral enlargement, and immediately followed by a bulging outwards at the cartilages of the 7th, 8th, 9th, and 10th ribs, and that part of the abdomen contiguous to them, with a slight advance of the lower third of the sternum. This is abdominal breathing, because the abdomen moves first ; and is confined to motion of the base of the thorax. In women it is likewise symmetrical, commencing with a gentle heaving of the upper part of the thorax, more or less apparent ac cording to the fulness of the mamma:. This expansion commences with the 1st and next three ribs following each other in succession, accompanied with a slight elevation of the shoulders and a slight lateral enlargement'of the chest, which is immediately followed by a bulging outwards of the abdomen. So quick is this motion of the diaphragm after the ino-. tion of the ribs, that at times they appear to be synchronous, especially when the individual examined is conscious of the observation; though it is only an accommodating movement of the diaphragm: This is costal breathing, because the ribs move first, and the motion is chiefly confined to the apex of the thorax. Therefore that which is a healthy respiratory movement in women is pathological in men.