BIRDS. 343 



those which are most usually hollow, often also the vertebrae (with 

 the exception of the first cervical), the ribs, the scapulae, the clavi- 

 cles, the pelvis, the thigh-bones. Rarely, however, are the thigh- 

 bones hollow when the upper-arm-bones are not so. The radius 

 and ulna, tibia and fibula, as also the bones of the wings and feet 

 which succeed to these, are, on the other hand, almost always filled 

 with marrow, to which the genus Buceros, according to the obser- 

 vations of NITZSCH, forms a remarkable exception, in which even the 

 phalanges of the toes ar^ pneumatic 1 . The cranial and facial bones 

 receive the air not from the lungs, but in part immediately from the 

 Eustachian tube and the cavity of the tympanum 2 , in part from 

 the nasal cavities which conduct it to a space situated under the 

 eye, from whence it penetrates further into the cavities and cells of 

 those bones 3 . 



We have still, in this place, to speak of the wind-pipe (trachea) 

 of birds, a part of the respiratory apparatus which we consider in 

 the last instance in order that we may unite with it conveniently 



also his Observations on certain parts of the Animal (Economy, edited by R. OWEN, 

 London, 1837, pp. 176 186. For extensive investigations at a later period we are 

 indebted to NITZSCH Osteografische Beitrdge, Leipzig, 1811, s. I 62. ALBERS and 

 G. VROLIK observed that birds can breathe through the perforated or broken humerus 

 and so continue to live after the ordinary passage for the air has been interrupted by 

 compressing the wind-pipe; REIL'S Arckiv, vi. s. 469 490. Compare also JACQUEMIN 

 Recherches physiol. et anat. sur la respiration, Memoire sur la pneumaticite des Oiseaux, 

 etc., Nov. Act. Acad. Ccesar. Leop. Carol. Tom. xix. 1839, PI. 2, pp. 288 333, Tab. 

 5961. 



1 MECKEL'S Archivf. Anat. u. Physiol. 1826, s. 618 and foil. 



2 On the inside of the lower jaw, behind the articular surface for the quadrate bone, 

 is the aperture by which the air from the tympanic cavity has access to them. Here 

 is sometimes a membranous duct present which leads from the cavity of the tympanum 

 to the aperture ; in many singing birds this duct is replaced by a bony tube which was 

 discovered by NITZSCH and named siphonium; Osteogr. JBeitr. s. 30 32. In Apteryx t 

 an entirely abnormal genus of birds from New-Holland, where also the air-cells do not 

 extend into the abdominal cavity, the under jaw is the only bone in which any trace 

 of pneumatieity, elsewhere so common in birds, is met with ; R. OWEN Transact. Zool. 

 Soc. II. 4, p. 286. 



3 Whenever the use of the hollow bones of birds is discussed, the opinion offered 

 by CAMPER is usually the first that is considered, viz. that the air that has been warmed 

 and rarified diminishes the specific gravity of the bird and so makes it fitter for flying. 

 But it must not be forgotten, that young birds do not yet possess these cavities though 

 they fly very well, that many, especially small birds, have no hollow bones, and that 

 bats are able to fly without any such provision. 



