NEW VIEW OF THE MECHANISM OF RESPIRATION 



281 



The diaphragm may not inaptly be compared to half a ventricle, half a stomach, or half a bladder. It is more- 

 over endowed with similar movements — these movements being centripetal and centrifugal in character ; that is, it 

 can open and close or. in common parlance, relax and contract in virtue of its own inherent powers, independently 

 and as apart from other muscles. When it closes or contracts it enlarges the thoracic cavity at the expense of the 

 abdominal one. When it opens or relaxes it enlarges the abdominal cavity at the expense of the thoracic one. It 

 will be seen from this that both the thoracic and abdominal cavities are engaged in respiration. Further, and as 

 I shall show presently, the muscles forming the chest and the abdomen are likewise both engaged. All the muscles 

 display rhythmic movements. It has been customary hitherto when speaking of calm or normal breathing to 



Fig. 45. 



Fig. 46. 



Fig. 45. — Muscles of the human diaphragm as seen from above, a, Upper surface of the tenth dorsal vertebra ; b, section of the 

 lower extremity of the sternum ; c, segment of the ninth rib ; rf, orifice of the oesopliagus ; e, section of the aorta ; /, opening for the 

 vena cava ; g, middle portion of the oblique fibrous band which separates the opening for the vena cava from the orifices of the 

 oesophagus and the aorta ; />, i, j, the origins of the fibrous oblique band which forms the thoracic surface of the right leaf of the 

 diaphragm ; k, I, triangular expansion of the oblique fibrous band in the anterior middle leaf of the diaphragm ; m, middle aponeu- 

 rotic suture of the right and left leaves of the diaphragm blended with the triangular expansion of the oblique fibrous band ; n, 

 portion of the semi-circular posterior band which forms the external boundary of the vena cava ; 0, p, q, portion of the semi-circular 

 band in front of the oesophageal opening on the left leaf of the diaphragm ; r, aponeurotic bundle of the left leaf of the diaphragm ; 

 s, the hepatic arch of the diaphragm ; t, splenic portion of tlie left half of the diaphragm ; u, v, gastric portion of the left half of the 

 diaphragm (after Bourgery). 



Fig. 46. — Muscles of the human diaphragm as seen from below, a, Fourth lumbar vertebra sawn through ; J, tip of xiphoid 

 cartilage ; c, seventh costal cartilage ; d, eighth ditto ; c, ninth ditto ; /, tip of tenth costal cartilage ; g, tip of eleventh ditto ; h, ex- 

 pansion of tendon of right pillar (third vertebra) ; i, expansion of tendon of left pillar (second vertebra) ; j, crossing of the tendinous 

 fibres of the two pillars on the second vertebra; k, fibrous arch of the aortic opening; I, internal fibrous arch ; m, external ditto. 



Left side. — n. Band of insertion of the two arches to the second and third transverse apophyses of the second and third lumbar 

 vertebrae. 



Right side. — 0, Attachment by round ligament to the summit of the twelfth rib ; p, cesopliageal opening between the pillars ; 

 (jr, elliptical opening for the passage of the inferior vena cava; r, superior extremity of the psoas magnus (right side) ; .s, superior 

 extremity of the psoas parvus (right side) ; (, posterior aponeurosis of the transversalis muscle (after Bourgery). 



confine the respire, tory movements to the action of the thoracic muscles. I am, however, convinced from a careful 

 and extensive examination of the subject that no respiratory act can ever take place as apart from the co-operation 

 of the abdominal muscles. As a matter of fact, the thoracic and abdominal muscles are correlated and co-ordinated 

 and work together to a common end ; that end being the alternate increase and diminution of the thoracic and 

 abdominal cavities. 



When the thoracic muscles shorten or contract the abdominal muscles elongate or relax. The thoracic and 

 diaphragmatic muscles shorten or contract synchronously, and by their united movements increase the thorax in all 

 its diameters. The abdominal and diaphragmatic muscles elongate or relax when the thoracic and diaphragmatic 

 ones shorten or contract. All the muscles referred to form part of a compUcated rhythmical system. In the corre- 

 lated co-ordinated movements under consideration the lungs play a not unimportant part. 



In order fully to understand the respiratory movements in man it is necessary to regard the muscles of the whole 

 VOL. I. ? ^ 



