torn of the deepest vallies to a considerable height 

 above the summit of Chimbaraco, where the ba- 

 rometer must have been lower than ten inches ; 

 and he frequently observed it soaring at an ele- 

 vation six times higher than that of the clouds of 

 our atmosphere. 



The bones of birds, in so far as their air cells 

 are concerned, form two distinct systems, the 

 one being filled with air directly from the lungs, 

 the other immediately from the mouth and nose. 

 To the latter, the bones of the head, to the for- 

 mer, those of the trunk, and of the neck and extre- 

 mities belong. The openings admitting air into 

 the bones, as their connection with the lungs or 

 air-tubes renders necessary, are situated in con- 

 cealed parts, and in the extremities of the bones ; 

 and this circumstance, coupled with their small- 

 ness, makes their discovery so difficult, that in 

 many cases the minutest examination of the sur- 

 face of the bone is necessary to discover their 

 existence. In long bones, the openings of the 

 air cells are generally situated close to either ex- 

 tremity. In bones which exist in pairs, there is 

 commonly only one ; or where several exist, they 

 are so close together, as to be nearly united. 

 Sometimes the opening is oblique, so that a short 

 oblique canal is formed ; at others there is an 

 oblique groove, with a sieve-like base for the en- 

 trance of the air. The edges of the openings are 

 even smooth arid rounded, which gives them a 

 peculiarly regular appearance. Their shape is 

 either circular, oval or elliptical. Their breadth 



