MEMOIR OF CAMPER. 47 



pecially in birds of prey, all the bones which can 

 communicate with the chest or abdomen, are filled 

 with air, and I have demonstrated the foramina by 

 which the air regularly enters and issues, with the 

 respiration. The air which thus fills the cavities, 

 must necessarily become lighter, as affected by the 

 temperature of the body, so that the weight of the 

 animals must thus become specifically less than that 

 of the air, thereby enabling them to fly with much 

 greater facility." * 



He then remarks, that traces of these osseous air- 

 cells are to be found in some other animals, and that 

 there is an instance of it even in man, in the bony 

 protuberance behind the ear, which is filled with air, 

 received from the common air-passages ; and he 

 draws some conclusions respecting the use of the 

 marrow, the growth and reparation of bone, and the 

 formation of callus, which are important in a phy- 

 siological and pathological point of view. 



This interesting subject he prosecuted with great 

 ardour for a succession of years. As already stated, 

 lie immediately demonstrated, the discovery to his 

 class, and sent a memoir on the subject to the 

 Batavian Society of Rotterdam ; and next year 

 transmitted a paper to L' 'Academic des Sciences, 

 which afterwards appeared in its Transactions a 

 proof, as the Professor remarks, that at this epoch 

 no one had previously known this singular structure. 



* The Solan Goose ( Sula alia) will present one of the 

 most beautiful illustrations of this curious structure ED. 



