82 THE ANATOMY OF THE WEDDELL SEAL. 



requires the minimum of muscular effort. The differences between the adult human 

 male and female types of breathing are adaptations due to the avoidance of severe 

 muscular effort so long as a smaller effort will serve the purpose, and in my opinion 

 they result from the normal differences in the lower or diaphragmatic diameters of the 

 thoracic cavity in the two sexes. To a large extent these differences may be accounted 

 for by the width of the female false pelvis as compared with that of the male. Since 

 the abdomen proper (i.e. excluding the true pelvis) contains no organs which are not 

 common to both sexes, it follows that a wide false pelvis, by providing increased 

 accommodation in the lower abdominal regions, is naturally associated with a reduction 

 in the dimensions of the upper or diaphragmatic end of the abdomen. These conditions 

 make elevation of the sternal ribs more necessary in the female than in the male, whose 

 larger diaphragmatic thorax permits of ordinary breathing without the pronounced or 

 visible elevation of his sternal ribs, although their movement may become visible when- 

 ever the supply of air required calls for an extension of the elevating movement. 



In either sex, a change from the erect attitude to the horizontal (e.g. to the supine) 

 position is usually followed by the introduction of more or less of the respiratory 

 features of the opposite sex, owing to the temporary interference with the amount of 

 rib movement in common use when the ribs are unobstructed. 



(ROY. soc. EDIN. TRANS., VOL. XLVIII., 332.) 



