482 THE RESPIRATORY APPARATUS. 



series of openings the middle ones that conduct the air into the sternal 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 sum 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 vertebras ; 2, To all the 

 dorsal vertebras ; 3, To all the vertebral ribs. The vertebrae of the neck are aerated 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 inter transverse canals; 

 the median current 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, which enters them by very 

 small apertures situated at their spinal extremity. 



"The diaphragmatic reservoirs have no bony communications. The abdominal 

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

 femurs. The air traversing the sacrum, coccyx, and ileum, comes directly Irom 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 serated skeleton : 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 serated are the cervical 

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

 the Ostrich. Those serated in some classes only are : the furculum, clavicles, scapulae, 

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

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



STRUCTURE OP THE KESERVOIRS. The walls of these cavities are essentially formed by a 

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

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

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

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

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



MECHANISM OF RESPIRATION IN BIRDS. The anatomical arrangement described 

 above differs in so many respects from that existing in Mammals, that it ought to bring 

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

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

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

 in a general manner the signification of the special organisation this apparatus offers in 

 birds. 



We remark, in the first place, that the slight mobility of the vertebral ribs, and the 

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

 viscus during inspiration. And the entrance of air into the pulmonary tissue is not 

 due to this dilatation ; it is due to the dilatation of the diaphragmatic reservoirs ; the 

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

 superior ribs. The air is then drawn into their cavity after traversing the larger 

 bronchial tubes which open into them, and also after passing across a certain region of 

 the capillary network formed by the canaliculi, where it comes into mediate contact 

 with the blood, and is submitted to the necessary transformations. The atmosphere, 

 therefore, arrives in the diaphragmatic sacs partly pure and partly altered by its contact 

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

 introduction, traverses a second time the lung, and is thus respired once more before 

 being expelled from the body. It is, therefore, obvious that the hsematosic transforma- 

 tions accomplished in the lung take place during the two acts of respiration inspiration 

 and expiration. 



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



