vivisections he determined, that in inspir ation the internal intercostals, " simultane ously with the external layer, contract, swell, and wrinkle, become perpendicular and hard, with united lifting of the ribs in rotation, the turning of the lower border forwards, the protrusion of the sternum, the descent of the diaphragm," &c. On the other hand, he observed in " expiration, relaxation of the whole series of intercostal muscles, increased length and obliquity, increased distance be tween the spaces, relaxation of the diaphragm, repression of the sternum, the descent of the ribs, narrowing of the chest," &c.* It is curious to see that he makes the cubic space of the thorax diminish with the inter costal spaces widening. Nor do we wonder at his observing, in his vivisections, a contrac tion of both sets of these muscles, for he not only skinned his animals, but " cut down and destroyed the external layers of intercostals, to lay bare the internal layer.' "Besides I ap plied (says Haller) pain and fear, being more efficient than mere pain itself," by puncturing the diaphragm to cause dyspncea ! Under such circumstances — an animal tied down, divested of all superficial muscles, with a pierced chest, — in *" pain and fear," and writhing under the scalpel,—producing tetanic convulsions, and then a death-like relaxation from syncope, — surely in such a condition the action of the respiratory muscles, so sensitive to the least mental emotion, could not well be determined.
Although Haller appears positive, yet he concludes his controversy with a brilliant question,—a vivid picture of his master mind, Why has nature made two, rather than one set of intercostal muscles, if, indeed, the function of each is the same?" Haller's views have, however, prevailed to this day, and are still taught in our schools. Some authors have assigned but little to these muscles, counting them as mere associate muscles ; others, that they are " wholly and solely" to form the thoracic parietes ; others that they are rather movers of the spine.
Dr. John Barclay, a standing authority, observes, that the supposition of the two sets being antagonists in their actionr "is now ob solete," and must " have been formed by the very witchcraft of imagination, in defiance of all observation and experiment." Lastly, Dr. Sibson has made a commu nication upon this subject. He observes, that " the scaleni invariably act during the whole time of inspiration ;" and that the function of the intercostal muscles is complicated ; thus, " the external intercostals, between the thoracic set of ribs, are throughout inspiratory; those portions between their cartilages are expiratory, between the diaphragmatic set of ribs they are inspiratory behind, expiratory to the side and in front, and between their cartilages they are inspiratory ; between the intermediate set of ribs they are for the most part slightly in spiratory between the ribs, and expiratory in front between the cartilages." " The internal intercostals of the thoracic ribs are expiratory behind and inspiratory in front, if the ribs approach there, and are in spiratory between the costal cartilages. Be tween the diaphragmatic and intermediate set of ribs, and between the cartilages, they are thought expiratory."# From this view of Dr. Sibson's, we venture to gather, that different fibres of the same layer of intercostal muscle have diametrically opposite actions. We do not understand upon what ground it can be demonstrated that one muscle having a given action between two ribs, shall, between the same ribs, and observing the same obliquity and same attachments, present a directly con trary action; the conditions are the same, and therefore the action must be the same. These
views, however, of Dr. Sibson, in the paper in question, are not borne out by the narra tion of any experimental facts. Insufflation on the dead body is not the movement of inspiration in the living subject. It is better to assign to these muscles the terms of ele vators or depressors of the ribs, instead of inspiratory and expiratory muscles.
All these observers, as far as we have seen, pre-suppose that the 1st rib is fixed by the scaleni (this is the view now taught) ; and that according to the fixing of the 1st rib, all the intercostal muscles are either elevators or depressors of the ribs. It is curious to contemplate that, out of elements so few, two ribs and two muscles, opinions so contrary should be held with regard to the action of these muscles. They have nevertheless an action as definite as any other muscle in the body.
We may here observe, that, although the chest is conical, the ribs segments of circles, and the spine mobile, yet treating them as planes and lines will not lead to error. Two parallel bars, rotating on a centre, will increase and decrease the perpendicular distance be tween them ; so they will, if curved like the ribs. This we have determined by experiment.
Although the rib has two movements, ele vation and rotation, yet these are associates, and do not obstruct each other. We shall employ the same diagrams as used by Dr. Barclay, when describing the same muscles.
The intercostal muscles act as a force be tween two moveable ribs or levers ; therefore let us consider — 1st. The movement of such levers, when rotating.
2nd. The effect of forces, oblique, perpen dicular, and decussating, upon such levers. 1st. The movement of the levers. — Let fig. 677. A represent a series of parallel bars, allowing of free rotation upon a rigid per pendicular body A a ; let the free extremities of these bars be kept apart, so that the bars may at all times be parallel to each other. In this condition a certain distance exists between the bars, and a certain distance be tween their free extremities and the perpen dicular body A a. Lets represent the same bars moved into another position, resembling that of the ribs ; in this position, the two conditions seen at A are altered. The perpendicular distances between the bars are diminished, and the distance between the free extremities of the bars and the body a b is likewise diminished. If the direction of this motion were still continued, the bars would ultimately touch each other, and their free extremities would be still nearer to the body s b. But let the bars be elevated, as in c c, and the same condition obtains as in the bars at s b, viz., they approximate each other, and the free ends come nearer to the body, c c. In this case the bars only have moved ; but the same effect can be obtained without moving the bars. Let A B (fig. 678.) be two bars at their maximum distance, while horizontal; at a b, and a' they have nearly attained their minimum perpendicular distances, though still hori zontal, because the rigid bodies c c and c' c' have been moved respectively. Now, if we join these hree last figures into one, as in fig. 679., an then move the bars simulta neously, some bars will approximate each other, whilst others will recede. The superior four are at their maximum perpendicular dis tance from each other ; while the 4th, 5th, and 6th are at a medium perpendicular dis tance, and the 6th, 7th, and 8th bars at their minimum distance.