216 



The above list of thirtj'-five birds (eiglit'of them foreign) includes 

 eight rapacious ; of these the Falconidse had air in the humeri, fe- 

 niora, and bones of the truiik. The tbur Ovvls, Strigidae, had air only 

 in the humeri. Of the twelve passerine birds the Carrion Crow, the 

 Jay, and the Tits had air oidy in the humeri ; vvhilst the remaining 

 seven, including five birds of passage, had no air in the bones. The 

 humeri of the Impeyan Pheasant were hollow. In the four climbers 

 the humeri contained air, but the femora vvere fuU of marrow. Of 

 the three \Vaders, the Turnstoue had the bones of the Umbsfree from 

 air, but the humeri of the Heron and Sains Crane were hollow. In 

 three of the web-footed birds, the geese and ducks had hollow 

 humeri, but the other four birds were without air in tlie hones of 

 the extremities. So that only five Falconidee of the above thirty- 

 five birds, had air in the Umbs ; the arm-bones of nineteen were 

 honow, and in twelve the limb-bones contained marrow. 



General Summary. — Adding these specimens to the fifty-two be- 

 fore described, the deduetion is as follows. Air in many of the 

 bones, 5 (Falconidse) ; air in the humeri and not in the inferior 

 extremities, 39 ; no air in the extremities, and probably in none of 

 the other bones, 48. I say probably, because I have not inspected 

 the trunk bones in all ; but in the Swallow, Martin, Šnipe, and 

 many birds of passage, I have found all the bones fiUed with marrow ; 

 and I infer that when the bones of the limbs contain no air, that 

 those of the trunk are also air-less. 



It vd\\ be remarked that I have spoken chiefly of the bones of the 

 extremities ; but in many birds that have air in the humeri and femora, 

 the sternum, clavicles, scapulee, furcula and vertebrse are also sup- 

 plied with this fluid. In the sternum, the air-holes are seen along 

 the base of the keel ; in some birds one air-hole only is present ; in 

 others, many exist, giving this part a cribriforni appearance ; the 

 vertebrae, too, of some birds (especially the Falconidae), as shown by 

 a section of the spine of the Golden Eagle (^A. chrysa'ėta), are com- 

 posed of a beautiful net-work of bone, rendering them extremely 

 light. 



The fact that I am especially anxious to bring before the Society 

 is, that in no bird that I have inspected did the bones of the extre- 

 mities beyond the humeri and femora contain air. 



Air-sačs inthe thoracic and abdominal cavities. — I have examined 

 these in the various classes of birds, and have found a greąt resem- 

 blance in all. They are mostly larger in high-flying birds and in 

 those of long and rapid flight. The best mode of inspecting these 

 cavities, which are formed by doublings of the pleurai or peritoneal 

 membranes, is to inflate them in the dead bird by means of a blow- 

 pipe inserted in the trachea. A ligature is then placed upon the air- 

 tube, and the body of the skinned bird exposed to a slow heat for 

 a few hours ; the membranes are by this means rendered dry and 

 stiff, so that the thoracic and abdominal viscera may be removed. 

 The body of the Long-eared Owl {S. otus) on the table has been 

 thus treated, and many of the air-sacs are plainly seen. But let me 

 describe more minutely the situation and form of these sacs in a ievf 



