Pigeon- or chicken-breast. —This is a mal formation quite distinct from any of the above mentioned, always affecting the sternal region in particular. An explanation of this curious disease has attracted the attention of Mr. Shaw, to whom we are indebted for the following remarks.* He noticed the effects produced upon the thorax by violent efforts of breathing in a child with croup. If we watch, says Mr. Shaw, the motions of the thorax in a young patient who is in danger of suffocation from an obstruction in the wind-pipe, we shall perceive that at each inspiration, while the superior ribs and sternum are raised and protruded as in com mon costal breathing, the lower ribs are, at first, flattened, and then drawn inwards, so as to produce a deep indentation on both sides. The depression is greatest in the line of junction of the ribs with their cartilages ; it is as if a band had been tied tightly round the waist, or resembles the indentation near the margin of the chest, often seen in women from tight lacing. The constriction lasts during inspiration; in expiration, the ribs by their elasticity flap out and recover their form. That the lower ribs should be drawn inwards in the act of inspiration, diminishing the area of the chest at a time when their natural motion should enlarge it, will be un derstood by considering the relative conditions of the thorax and the lungs in the laboured respiration which arises from obstruction in the wind-pipe. Under the sense of impend ing suffocation, the young patient instinctively struggles to enlarge the cavity of the chest to its greatest capacity ; but, while that effort is making, the quantity of air that passes into the lungs is very small, because of the obstruction in the larynx or trachea : a portion of air may reach the air-cells at the apex where the bronchial tubes are short, but little or none penetrates so far as the base of the lungs ; consequently the lungs are imperfectly dilated. If the child succeed in enlarging the area of the chest in proportion to its powerful efforts, while the lungs were at the same time but partially dilated, it would follow that a vacuum would be produced in the space between the parietes of the thorax and lungs. But owing to the great flexibility of the ribs near the lower margin of the thorax in childhood, the atmospheric pressure overcomes the action of the muscles, and thrusts in the sides so as to preserve the balance of the air within and that without : in common language, the walls of the chest on each side are " sucked " inwards, like the valve in a pair of bellows.
When we look at the general shape of the chest during the continuation of the con striction, we perceive at once a resemblance to the pigeon-breast deformity ; there is in both the same protrusion of the sternum, and the same depression of the cartilages on each side.
The question therefore arises, can the de formity have a similar origin to the change in the figure of the chest which is caused by difficult respiration ? Dupuytren wrote a memoir upon this form of distortion, and he has shown that difficult respiration and pigeon breast deformity are frequently associated to gether, so that he has almost constantly found that patients who are pigeon-breasted have at the same time enlargement of the tonsils ; but Dupuytren does not profess to explain why the two complaints should go together.
Some years ago Mr. Shaw had under his care a little boy with greatly enlarged tonsils, which were very low down in the throat, owing, as it appeared, to their having got within the grasp of the constrictor muscles of the pharynx. He had constant dyspncea, and occasional fits of suffocation, in one of which Mr. Shaw performed laryngotomy: on his admission into the hospital, and for several weeks afterwards, it was observed that he had the " pigeon-breast " form of chest ; but after his tonsils were excised, and his breathing had been perfectly free for some time, the sternum subsided to its proper level, and the thorax recovered its natural shape. These facts prove that a connection, like cause and effect, exists between obstruction of the air passages and pigeon-breast de formity. It is not necessary that such impe diments should be so great as to produce strongly marked symptoms of dyspncea ; for, while the distortion is being produced the child is growing,—both the size and shape of the chest are undergoing a natural change. Mr. Shaw justly considers it quite possible that a cause which may have very slight in fluence in changing the figure of the thorax, if operating only for a week or a month, will, if continued longer, disturb and modify the pro cess of growth ; so that after intervals of half years or years, a decided effect will be exhibited in the form of the chest. It is not impossible that continued disease in the air passages of children, which may fail to attract much at tention, or at least may not be thought capa ble of producing distortion, may nevertheless gradually and insidiously give rise to the per manent deformity of "pigeon-breast" Mr. Shaw particularly refers to enlargement of the tonsils, attended even with slight incon venience; to enlargement of the lymphatic glands in the course of the trachea or bronchi ; to pressure upon the trachea by the thymus gland, when later than natural in being ab sorbed, or when hypertrophied ; and to mor bid thickening of the mucous membrane- of the larynx, or of the trachea and bronchi succeeding croup or cynanche pharyngea. We concur with these views upon this sub ject, the more so as we likewise have noticed the pigeon-breast in children where enlarged tonsils have been present. We must not imagine from this that, where there is dyspncea, there we shall always find the deformity in question ; for difficult breathing may be caused by other circumstances than those which dis turb the counter-pressure of the atmosphere in the thorax.
IV. Dimensions of the thorax.—The mea surement of the thorax may be considered externally and internally ; and, what is most remarkable, the one class of measurements may not have any relation to the other class. Moreover, the external measurements bear a certain proportion to the whole frame, whilst the internal do not.
(a) External measurements of the thorax.— The external dimensions of the thorax differ much in different men ; this is obvious to all. There is the broad-chested and the nar row-chested man. Mr. Brent has calculated, from an extensive number of observations, the following proportions, which we arrange thus :— Thus, by taking the most perfectly propor tioned chests, either from living figures or from the classical athlete of ancient sculptures, the following is the result.