GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 371 



costals, with those portions of the. internal intercostals which pass between 

 the cartilages, the levatores costarum, and a portion of the triangularis sterni, 

 all of which have the same action, that of elevating the ribs. On the other 

 hand, the thoracic Expiratory muscles are the proper costal portion of the 

 internal intercostals, with the infracostals, and a part of the triangularis 

 sterni. The expiratory movement Avill be assisted also by the abdominal 

 muscles, which antagonize the diaphragm by pressing back the abdominal 

 viscera, and thus causing its ascent so soon as it has become relaxed. There 

 are many accessory muscles, however, which take a share in violent respira- 

 tory movements, both inspiratory and expiratory. Thus all the muscles 

 which elevate the scapula, may act through it upon the ribs the steruo- 

 mastoid raises the clavicle, and the scaleui act directly upon the first rib ; 

 whilst all those which erect the spine fix more perfectly the origins of these 

 and other muscles which are to act upon the thorax. So, again, the expi- 

 ratory movement is aided by the longissimus dorsi, sacro-lutnbalis, and other 

 muscles which tend to depress the ribs. In difficult respiration, almost every 

 muscle in the body is made in some way subservient to the distension of the 

 chest ; thus, a patient suffering under urgent dyspnoea instinctively lays hold 

 of some fixed object, so as to prevent his upper extremities from moving ; 

 and thus his scapula becomes a fixed point, from which the pectorales (major 

 and minor) and serratus magnus can aid in elevating the ribs. The move- 

 ments of the heart have a slight influence on the lungs, the systole aiding 

 inspiration, the diastole expiration. 1 



290. The extent of movement of the several parts of the chest during the 

 respiratory acts maybe registered by an instrument suggested by Dr. Burdon- 

 Sauderson, 2 and named by him the "recording stethometer." From ex- 

 periments made with this instrument, he finds that in the ordinary respiration 

 of a healthy muscular young man aged twenty -two, the upper antero-posterior 

 diameter, which was equal to 146 mm., varied one millimetre; the lower 

 sternal diameter, which equalled 203 millimetres, varied 1.5 to 1.8 mm. ; and 

 the transverse costal diameter at the level of the eighth rib, which equalled 

 228 mm., varied 1.7 to 2.0 mm. In forced respiration the variations of the 

 antero-posterior diameters of the upper part of the chest were much more 

 extensive, the ends of the upper ribs moving horizontally forward i.e., in 

 a plane parallel to the middle plane of the body, from 12-30 millimetres: 

 the advance of the third rib being greater by several millimetres than that 

 of the fifth, and this Dr. Ransome attributes to an actual bending of the 

 ribs. 3 The extent of the respiratory movements is affected by various mor- 

 bid conditions. Thus, when dislocation of the spine takes place above the 

 origin of the intercostal nerves, but below that of the phrenic, so that the 



tion, as also in forced expiration, whilst ordinary expiration is accomplished alto- 

 gether by elasticity, and not by muscular effort at all. Aeby (Lehrbuch, 1871, p. 

 379) hold's that both sets of muscles approximate the adjoining ribs, but whether this 

 occasions an elevation or depression of the whole series is dependent on the coinci- 

 dent action of other muscles. 5. Mayo and Magendie regarded both sets of muscles 

 as at once expiratory and inspiratory in their action. Lastly, Van Helmont, Aran- 

 tius, Cruveilhier, Kiiss, and Jobelin considered that both sets of muscles are passive 

 in the movements of respiration, and simply form an immovable wall to the chest, 

 or rather they contract, not to produce the movements of inspiration or expiration, 

 but to resist at both periods the pressure either of the external or of the internal air. 



1 See Voit and Lessen, Zeitschrift fur Biologie, Bd. i; Ceradini, Verhand. des 

 natur.-hist.-med. Vereins zu Heidelberg, 1869. Also Landois, who, however, holds 

 a different opinion (Berlin Klin. Wocbens., 1870). 



2 Handbook for the Physiological Laboratory, p. 291. 



3 See Arthur Ransome, On the Mechanical Conditions of the Respiratory Move- 

 ments in Man, Proceed. Roy. Soc., Nov. 1st, 1872. 



