Action of the intercostal muscles. — There is, probably, no subject in the whole range of science which has excited more violent con tention and acrimonious dispute, than that of the action of the intercostal muscles. The illustrious and learned Haller could not enter this field of inquiry without pausing to ob serve : " Let it be allowed me to deplore, among the miseries of human life, that such anger and bitter quarrels should be forced upon us on account of matters wherein we are so little personally Yet, strange to say, Haller opposed with extreme violence his contemporary Hamber ger, whose investigations on this subject, though still extant, fell, consequently, into oblivion.
We know not who discovered the two sets of intercostals. There appears to be no ac count of them prior to Galen, A. D. 131. He observes, "the intercostal muscles help the midriff, that they might draw the chest in ward."t Albinus (A.D. 1770) considered that both the internal and external layers "raise the ribs." H. Cooke, a learned compiler of 1651, believed, they " constrained and dilated the chest," —" that the external layers bear down the ribs, and that the internal separate the ribs, so enlarging the thoracic cavity." § Strange to say, after this Cooke divests these muscles of all thoracic motion whatever.
In 1685 it was the received opinion that the external layer dilated, and that the inter nal layer contracted the thorax II John Al phonso Borelli led the way to a different opinion, which prevailed amongst most phy siological writers. He believed, from mathe matical reasoning, that " the fibres crossing each other produced only one effect, viz., the drawing of the ribs together," —acting in the diagonal of the decussation. It is curious that he never considered the proba bility of the two forces acting separately, as other antagonising muscles can do. ¶ W. Cheselden believed that both these muscles dilated the thorax, acting as elevators of the ribs, when the 1st rib was fixed by the scaleni and serratus posticus posterior.** Cooke follows the views of Cheselden and Borelli.ft Benjamin Hoadly takes another view ; and, in so doing, illustrates the subject with diagrams, and comes to the conclusion that the external layers elevate, and that the internal depress the ribs ; and that their com bined action is to arrest the respiratory move ment at will. He also says, "neither range can by their action push the ribs asunder."I$ Winslow agrees with Borelli : presupposing, as usual, that the first rib is fixed. §§ Still the subject continued to be warmly dis puted, when Haller published a controversial paper in 1746. In his "Elements,"he treats the subject at length, siding with those whom he thinks are right, and confirming the same by many direct experiments.* Haller's view is, that the external layers elevate the ribs, be cause their superior attachment is nearer the vertebrm than their inferior one. Franciscus
J3oissier de Sauvages agrees with him ; and the same is held by the majority, yet some doubt it.
His opinion touching the internal layer is, that they likewise act as associates and ele vators of the ribs with the external layer, be cause " their superior attachment is nearer the sternum, and further from that bone in the lower ones ;" likewise, that " that por tion of the internal layer placed between the bony parts of the ribs, cannot have a diffe rent action from that portion placed between the cartilages." Joh. Swammerdam, Francis Bayle, J. Willielmus Pauli, Christianus Vater, Francis Nicholls, J. Fredericus Schreiber, differ from this, believing that the internal layers draw down the ribs.
Now follows a sharp antagonist to Haller, viz. Hamberger, whose disputes with Haller we gather from Haller's writings, and not from Hamberger's writings.
Hamberger breaks out with an entirely new view, which excites Haller to controversy.t Hamberger, says Haller t, believes that the external intercostal muscles have one action, —that they would raise the sternum : " that the internal layer would depress it." Ham berger makes a machine " to demonstrate, that when the ribs are raised by these muscles their intervals are dilated ; when depressed, on the contrary, they are diminished." He furthermore gives, as his own discovery, that " the internal intercostals conjoining the os seous portions of the ribs, and that portion which is between the cartilages, will raise them, and are therefore associated in action with the external layer." Hamberger was the first to assign a double action to the same class of muscles : he likewise believed that the whole ribs were lifted simultaneously.§ Haller disputes the validity of Hamberger's experiments, upon the ground of his not con sidering the relative mobility of the first and second rib ; because, says Haller, if the de pressing power of the intercostal muscles is to the first rib as 20, the elevating power on the second rib, by reason of the difference of length and mobility, is as 380, nearly nine teen times greater ; and the lower rib is to each superior rib, as far as .the seventh, more moveable, in the ratio of 109 to 79.11 We cannot see, with Haller, how the ten dency of action of a muscle can be affected by the degree of mobility of a joint ; for it is not necessary to the direction of the action of a muscle that a bone should move. Haller also denies that the two crossing fibres lengthen and shorten inversely to each other ; or that the intercostal spaces widen by their action. Haller performed many experiments ; he ap plied strings to the ribs of a wet preparation, representing the muscles, and pulled the strings, and the intercostal spaces diminished.