1046 



THORAX. 



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. 

 By 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 lap- 

 plied (says Haller) pain and fear, being more 

 efficient than mere pain itself," by puncturing 

 the diaphragm to cause dyspnoea! 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?"f 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." t 



Lastly, Dr. Sibson has made a commu- 



* El. Phys. ib. p. 43. 

 t Ib. p. 44. 



I Barclay " On Muscular Motion," 8vo. Ed. 1808, 

 pp. 533, 534. 



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 



Tr. Phil., Pt. 4, 1846, pp. 543, 544. 



