566 RESPIRATORY APPARATUS IN BIRDS 



by small openings at their inferior extremities. To smn up, eight bones, without 

 reckoning the sternal ribs, whose number varies, receive the air which tills them 

 from the thoracic reservoir. 



"The cervical reservoirs conduct the air. 1. To all the cervical vertebrae. 

 2. To all the dorsal vertebras. 3. To all the vertebral ribs. The vertebrae of 

 the neck are crated 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 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 abdo- 

 minal 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 from the supra-renal prolongations, and that filling the femoral 

 cavity from the femoral prolongations. In this enumeration of the communi- 

 cations between the skeleton and the respiratory apparatus, we have taken as 

 a type the most aerated 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 serif erous 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 s6 in the Ostrich. Those crated in some classes only 

 are : the furculum, clavicles, scapulae, vertebral and sternal ribs, the sacrum, 

 coccyx, and femurs. And the bones which are never aerated are those of the 

 forearm and hand, the leg and foot." 



Structure of the Reservoirs. — The walls of these cavities are essen- 

 tially 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 pul- 

 monary, but to the general circulation, the arteries being derived from the 

 aorta, and the veins opening directly or indirectly into the venae 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 organization this apparatus oifers 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 



