204 ANATOMY OF THE DOMESTIC FOWL 



Summary of Bones Supplied by Each Air-sac. — The thoracic air- 

 sac communicates on each side of the thorax with twelve bones, 

 including the four sternal ribs. It supphes air to the clavicles, which 

 are perforated at both their extremities, and to the coracoids, which 

 are perforated just below their scapular extremity. The sternum 

 is supplied through two series of openings, the middle ones that 

 conduct air into the sternal ridge and the lateral ones, eight in 

 number and very small, correspond to the intercostal spaces. The 

 sternal ribs are penetrated by small foramina at their inferior ex- 

 tremities. From the subscapular extension the scapulae receive air 

 through one or two foramina at their anterior extremity. The 

 humeral prolongation supplies the humerus through a foramen 

 located at .the upper edge of the hvuneral fossa, at the infero-intemal 

 part of the articular head. 



The cervical air-sac furnishes air to all the cervical vertebrae, to 

 all the dorsal vertebrae, and to all the vertebral ribs. The anterior 

 parts of the vertebras of the neck are supplied with air through the 

 passage accommodating the vertebral artery. The posterior parts 

 of the vertebrae are supplied by extensions from the interspinal 

 canal. The first extensions obtain entrance to the', anterior seg- 

 ments by one or more openings of the inner wall of the intertrans- 

 verse canals; the median extensions penetrate the posterior seg- 

 ments by two openings, a right and a left, situated on the inner wall 

 of those segments. The first dorsal vertebra is supplied with air 

 in the same manner, by the middle and the lateral canals of the 

 neck. This air, after passing through the first vertebra, leaves by 

 a lateral exit to enter a small air-sac. From this it passes into the 

 superior part of the second vertebra, escapes from this through 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 openings located on their spinal 

 extremities. 



The diaphragmatic air-sacs do not have communications with the 

 bones. 



The abdominal air-sacs commOnicate with the sacrum, the 

 coccygeal vertebrae, the iliac bones, and the femurs. The air 

 passing through the sacrum, the coccyx, and the ihum comes directly 

 from the supra-renal extensions; the air which fills the femoral cavity 

 comes from the femoral extensions. 



In some birds these air spaces are more greatly developed than in 



