370 OF RESPIRATION. 



ribs ; for whilst, in the undilated state of the thorax, the ribs form an angle 

 with their cartilages, which becomes less and less obtuse as we pass from the 

 first rib downwards, the elevation of the ribs tends to bring them and their 

 cartilages more nearly into a line, and thus separates them more widely from 

 the median plane, and at the same time causes them to push forward the 



FIG. 162. 



Tracing of the respiratory movements in a healthy man, taken by M. Marey's Pneumograph. The 

 down-stroke represents the act of inspiration, the up-stroke that of expiration. The undulations at 

 the apex of the curve, which represents the period of pause of Longet, are due to the cardiac beats. 



sternum. Owing to the greater length of the lower true ribs, and the 

 greater obliquity of their junction with their cartilages, both these changes 

 are more considerable in the lower part of the thorax than in the upper; 

 and this is especially the case in adult men, whose respiration has been des- 

 ignated as " inferior costal," whilst in females the mobility of the first rib 

 and of the whole of the upper part of the thorax is greater, so that their 

 respiration may be designated as "superior costal." The thoracic muscles 

 whose contraction participates, with the diaphragm, in the ordinary move- 

 ments of Inspiration, are, according to Dr. Hutchinsou, 1 the external inter- 



1 Op. cit., p. 105,5 See also Cleland, Journal of Anat. and Physiol., vol. i, 18G7, 

 p. 209. There is probably no point in the whole range of physiology respecting which 

 such different opinions have been entertained by good observers as upon the action 

 of the intercostal muscles, and it may be instructive to give the following enumora- 

 tion of them, drawn from Beau and Massiat (Arehiv. Gen. de Med., 1842), Kiiss 

 (Physiologic, 1873, p. 343), Budge (Compendium de Physiol. Humain, 1874, p. 55), 

 and Colin (Traite de Physiologic Comparee, 1873, p. 251 et seq.) : 1. Both the exter- 

 nal and internal intercostals are inspiratory muscles ( Borelli, Senac, Boerhaave, Wins- 

 low, Haller, Cuvier, Colin, Wiindt, Duchenne, Duval). Duchenne supports his 

 opinion by reference to a case in which all the respiratory muscles were paralyzed 

 except the intercostals, and yet in which respiration was maintained ; Duval rests 

 his upon experiments made on decapitated criminals shortly after death. 2. Both 

 sets of muscles are expiratory (Vesalius, Diemerbrock, Sabatier, Beau and .Massiat, 

 Longet). This view rests on the fact that in vivisections the muscles may be seen 

 to contract in forced expiration, as in coughing or crying out. Moreover, the inter- 

 ruMals are present in Birds, in which the act of expiration alone is due to muscular 

 effort. 3. The external intercostals are expiratory, the internal, respiratory muscles 

 (Galen, Bartholinus). 4. The external intercostals are, inspiratory. The internal, 

 expiratory muscles (Spigelius, Vesling, Hamberger, and, with some modifi cation j 

 Sibson, Herrmann, and Cleland). According to Sibson the external intercostals are 

 inspiratory, except at their anterior part, in the five inferior intercostal spaces; the 

 internal intercostals are inspiratory in the anterior part of the five first span's, but 

 have elsewhere, an expiratory action. Herrmann observes that the external muscles 

 are inspiratory where they are attached to the osseous portions of the ribs, the in- 

 ternal where attached to the cartilaginous portions ; but as this corresponds to the 

 chief act inn of the two sets of fibres both may be regarded as inspiratory muscles 

 Cleland (Letter to Editor) remarks similarly that the external and anterior fibres of 

 the internal intercostals are most advantageously disposed for elevating the rilis, and 

 that the remaining intercostals are most advantageously placed for depressing the 

 ribs; but that all the intercostuls are capable of giving some assistance in inspira- 



