290 



DESIGN IN NATURE 



Neither the air nor the 



relation to the chest which the blood holds to the several compartments of the heart, 

 blood act as extraneous stimuli in the ordinary sense. 



Plate Ixxviii., and Figs. 50 to M inclusive, show that the muscles of the human trunk, like those of the 

 ventricles of the mammalian heart, run in every direction, namely, vertically, slightly obhquely, obliquely, and trans- 

 versely. These remarks apply to the anterior, posterior, and lateral aspects of the trunk. The muscles are also 



Flu. 5t). 



Fig. 57. 



Fig. 56. — Photograpli of the ventral aspect of|aii atlilete with hi.s arms hanging down holding his breath after having taken a full 

 inspiration. The chest muscles are firmly contracted and the chest is fully expanded in all its diameters ; the dome-shaped diaphragm, 

 although concealed, is also contracted and flattened in a downward direction. The capacity of the chest is increased at the expense of 

 the abdominal cavity. The chest projects and the abdomen recedes. The abdominal viscera are compressed between the under surface 

 of the diaphragm and the upper surface of the pelvis, notwithstanding the relaxed condition of the recti abdominis and of the external, 

 internal, and transversalis aljdominis. 



The lumpy condition of the muscles of the front of the chest testifies that the lower portion of the pectoralis major, the pectoralis 

 minor, and external and internal intercostal muscles are in a state of active contraction ; whereas the smooth appearance presented by 

 the abdominal muscles (especially the recti abdominis) attests an opposite condition. The thoracic muscles are seen relaxed and the 

 abdominal ones firmly contracted in a complemental photograph (Fig. 57), where a full expiration has been made. The alternate 

 opening and closing centrifugal and centripetal res]iiratory movements occurring in the chest and abdomen respectively can readily be 

 studied on the living subject. The rule is, that ■\\hen tlie muscles of the chest open or relax, those of the alidomen close or contract, 

 and vice versd (the Author). 



Fig. 57.— Photograph of the ventral surface of an athlete with his arms raised who has made a full expiration. This photo- 

 graph shows exactly the opposite conditions to those seen in the photograph just described (see Fig. 56). In this photograph the 

 chest muscles are all open or relaxed by centrifugal movements. The muscles of the abdomen, on the contrary, are all closed or con- 

 tracted by centripetal movements. In this case, the surface of the chest is smooth owing to the muscles being relaxed and flaccid, 

 whereas those of the abdomen are lumpy because of their being firmly closed or contracted. This is especially the case in the recti 

 abdominis muscles, which stand boldly out on either side of the linea alba. 



The diaphragm in this photograph is arched upwards into the cavity of the thorax by a centrifugal movement. By these means 

 the cavity of the chest is diminished and that of the abdomen increased. The two photographs under "consideration conclusively prove 

 the opening and rlusing consentaneous movements which alternately occur in the thoracic and abdominal muscles durino- respiration. 

 The th(jracic and abdominal movements are both yilal in their nature (the Author). ° 



