76 PROFESSOR DAVID HEPBURN ON 



On the other hand, this flexibility of the chest becomes not only a drawback, but 

 may be an actual source of danger when the marine mammal comes on shore either by 

 intention or as the result of accident. Thus it is well known that a cetacean dies when 

 it runs aground, not necessarily by starvation, but because it is suffocated, since the 

 flexibility of its chest-wall renders respiratory movements impossible under the superin- 

 cumbent weight of its body. 



The leader of the Scottish National Antarctic Expedition made very careful observa- 

 tions on the attitude of seals when they left the water and resorted to the ice, and he 

 noted that they do not assume positions which would hamper their chest movements. 

 Thus they recline on the side when asleep so as to leave the movements of one side of 

 the chest unimpeded, while at other times their common attitude is to lie prone with 

 the chest raised off the ground by the short fore limbs. Considerations of this kind lead 

 to the conclusion that respiration, but more especially the act of inspiration, can be 

 seriously impeded or even rendered impossible by the weight of the animal's own body. 

 That free inspiratory movement of the chest-wall in man may be hampered by the 

 weight of his body may be readily observed in the case of an operatic singer who, by 

 the exigencies of his performance, is called upon to sing in the supine position ; for 

 although in this position he can fill his lungs sufficiently for ordinary respiration, 

 yet he cannot inspire deep enough for effective vocalisation. Clearly, therefore, the 

 respiratory mechanism is affected by the attitude of the individual as well as by the 

 surrounding medium, air or water, in which the animal performs the necessary 

 respiratory movements. 



There can be no doubt that, whatever the natural attitude of the mammal may be, 

 or whatever its habitat, the ordinary movements of inspiration and expiration are carried 

 out with the minimum expenditure of effort consistent with the amount of air required 

 for each respiratory act. On the other hand, special circumstances may call for 

 additional or extraordinary efforts both as regards inspiration and expiration. The 

 discussion of respiratory movements is usually left, and by many observers considered 

 properly left, to the physiologist ; but as these movements are entirely dependent 

 upon a definite mechanism in which the muscular arrangements play an important 

 part, they cannot fairly be excluded from the province of the anatomist, and it is 

 from the standpoint of structure that I propose to offer some observations which 

 seem warranted by the conditions I have seen in the seal under consideration, as well 

 as in the porpoise. 



It may be well in the first instance to deal with the lungs themselves ; and, as the 

 condition in which I found them has already been stated, it will only be necessary to 

 add that, except for the presence of the azygos lobe on the right side, they corresponded 

 with the human lungs so far as the number and arrangement of fissures and lobes was 

 concerned. There is no reason to suppose that during the act of inspiration they would 

 inflate in a manner different from the lungs of man. Now, among the many interesting, 

 elaborate, and ingenious attempts to explain the respiratory act, none is more suggestive 



(ROY. soc. EDIN. TRANS., VOL. XLVIII., 326.) 



