46 



short. But tho most important peculiarity from a pathological 

 point of view remains to be noticed, the ahseiice of a pleura, which 

 exempts the animal from pleurisy, hydrothorax, and the danger of 

 wounds penetrating the Pleural Sac, thus materially reducing 

 the list of of thoracic disorders. When dissecting the chest 

 of an elephant I found that the lungs, instead of having their 

 surface covered by a smooth layer adapted to glide over a 

 corresponding lining membrane of the chest, were firmly adherent 

 by means of elastic tissue throughout the whole of their surface 

 to the walls of the chest ; I was struck with this anatomical 

 peculiarity but yet remembered an account of death of ele- 

 phants from pleurisy, thus evidently either my observations 

 were erroneous or the recorder of pleurisy in the elephant 

 had described what from the nature of things could not take 

 place. I found- that Owen and other observers had previously, 

 noted this remarkable anatomical peculiarity of the elephant, but 

 Miall and Greenwood, the latest observers, state "The visceral 

 and parietal layers of the pleura are closely connected together 

 by matted elastic tissue, while the pleural sac is at the same time 

 pretty generally adherent to the Thoracic wall on the one hand 

 and to the surface of the lungs on the other." I cannot help 

 thinking that these anatomists lead us into error when they speak 

 of the pleura and pleural sac as occurring in the elephant. The 

 lungs are but slightly lobulated, their parenchyma is plentiful 

 as in the lungs of the ox, their bronchi are only two in number 

 (not three as in the. ox) and the walls of the bronchial tubes in the 

 lungs are described as devoid of cartilages, which gives the whole 

 lung texture a peculiar softness under the knife. It is not hard 

 to explain why there is no pleura in the elephant. His mode of 

 life seldom subjects him to respiratory emergencies and his 

 organization is such that he does not require much blood oxy- 

 genation. Only when the respiratory passages are wide and ex- 

 pansible, so that a rush of air in broad current can rapidly dis- 

 tend the lungs and cause extensive motion of the lungs on the 

 avails of the chest is a pleura required — when the air enters 

 slowly through narrow passages, as in the elephant and birds, a 

 gradual expansion of the thoracic walls takes place and only such 

 motion between them and the surface of the lungs as can be met 

 by the yielding qualities of ordinary elastic tissue. As the respira- 



