482 TEE BESPIBATOBY APPARATUS. 



aeries of openinga — the middle ones that conduct the air into the eternal ridge, and the 

 lateral ones, very small, six to eight in number, corresponding to the intercostal spaces; 

 4, The scapulae, which offer one or more apertures at their anterior extremity, and receive 

 the air for the subscapular prolongation ; 5, The humerus, which obtains the air for 

 the humeral prolongation by a fossa situated at the inferior and internal part of its 

 articular head ; 6, The sternal ribs, which allow the atmosphere to penetrate by small 

 openings at their inferior extremities. To snm up, eight bones, without reckoning the 

 sternal ribs, whose number varies, receive the air which fills them from the thoracic 

 reservoir. 



" The cervical reservoirs conduct the air : 1, To all the cervical vertebrse ; 2, To all the 

 dorsal vertebrje ; 3, To all the vertebral ribs. The vertebrse of the neck are terated in 

 their anterior part by the currents which accompany the vertebral artery, and in their 

 posterior part by the interspinal current. The first obtain entrance to the anterior 

 segment by one or more orifices made in the inner wall of the intertransverse canals ; 

 the median ctirrent penetrates the posterior segment by two orifices, a right and left, 

 situated on the inner and medullary wall of that segment. The first vertebra of the 

 back is provided with air in the same manner, by the middle and lateral currents of the 

 neck. This air, after passing through the first vertebra, leaves by its lateral parts, to 

 enter a small sac ; from this it goes into the superior part of the second vertebra, escapes 

 from this by its lower portion, to be received into a lateral sac, and so on to the last dorsal 

 vertebra. These sacs also supply the vertebral ribs with air, wliioh enters them by very 

 smail apertures situated at their spinal extremity. 



" The diaphragmatic reservoirs have no bony communications. The abdominal 

 reservoirs supply : 1, The sacrum ; 2, The coccygeal vertebras ; 3, The iliac bones ; 4, The 

 femurs. The air traversing the sacrum, coccyx, and ileum, comes directly from the supra- 

 renal prolongations, and that filling the femoral cavity from the femoral prolongations. 

 In this enumeration of the communications between the skeleton and the respiratory 

 apparatus, we have taken as a type the most aerated skeletoji : that of diurnal birds of 

 prey, like the eagle, kite, hawk, etc. ; the bones which communicate with the air-sacs 

 are not so numerous in the other classes. In this respect, they may be ranged in three 

 categories : 1, Those which are aeriferous in all classes ; 2, Those in certain classes only ; 

 3, And those which are not so in any class. The bones always aerated are the cervical 

 and dorsal vertebrae, the sternum, and we may add the humerus, though it is not so in 

 the Ostrich. Those aerated in some classes only are : the furculum, clavicles, scapulse, 

 vertebral and sternal ribs, the sacrum, coccyx, and femurs. And the bones which are 

 never aerated are those of the fore-arm and hand, the leg and foot." 



Stbuoture op the Eeservoibs.— The walls of these cavities are essentially formed by a 

 thmcellulo-serous membrane, strengthened in some places by an external envelope of 

 elastic fibrous tissue. Long, thm blood-vessels are distributed to the substance of these 

 walls ; they do not belong to the pulmonary, but to the general circulation, the arteries 

 bemg derived from the aorta, and the veins opening directly or indirectly into the vense 

 cava. No lympljatics have been found in the air-sacs 



Meo^ism of Eespibation in BiRD8.-The anatomical arrangement described 

 above differs in so many respects from that existing in Mammals, that it ought to br'ne 

 about important modifications in the mechanism of respiration. It does not cd.me 

 withm our scope to write the history of these modifications; but we cannot dispense 

 with indicating, m a summary way, their principal characters, in order to make knowta 

 Srds^™^' '"'''"*'' signification of the special organisation this apparatus offers in , 



«^ w.f Tt^ 'f *'"' P"lPl^«?' tl^^V^e sl'gl^t >"«tility of the vertebral ribs, and the 

 adhesion of the lung to their inner face, only allows of a very slight dilatation of that 

 viscus dunng inspiration. And the entrance of air into the pulmonSv tissue L not 

 duetothisdilatation,- it is due, to the dilatation of the diaphra^arreserv4a ?he 

 position of these effectively admits of their expansion, by the play of the inferior on the 

 superior nbs. The air is then drawn into their iavity atir^ravers^g the Wer 

 bronchia tubes which open into them, and also after passing across a certfin region of 

 ^thX'^bl^nr ".'■'^ formed by the canaliculi, where it comes into med atefontect 

 with the blood, a,nd IS submitted to the necessary transformations I'he atmosnhere 

 i^fh r' lY'T ''V^^'^- di'^Pl'i-asniatic sacs partly pure and partly altered LtTcontact 

 with the blood. During expiration, it again resumes the course it followed on its 

 introduction, traverses a second time the lung and is thus resnltorl l„„o Z c 



being expelled from the body. It is, therefofe, obvils th^t SaematoTi^^^^^^^ 

 anrexprtfof '' " ''"' '"°^ ''^^ ^'^'^ ''""'^^ *^^ *™ -'^ of respS^ticS-CiXn 

 In studying the part that the other reservoirs play in this function, M. Sappey has 



