RESPIRATORY SYSTEM OF BIRDS. 215 



the spinous processes, the air passes into them directly from the 

 luno's. In the two or three lower cervical vertebrae the air-holes 

 are in the same situation, but receive the air from the lower 

 cervical or clavicular air-cells : in the remainder of these vertebras 

 the air-holes are situated within the canal lodging the vertebral 

 artery, and communicate with the lateral air-cells of the neck. 



The air-holes of the vertebral ribs are situated at the internal 

 surffice of their vertebral extremities, and appear, like those of 

 the contiguous vertebra?, to have an immediate communication 

 with the lungs. The sternal ribs have also internal cavities which 

 receive air from the lateral thoracic cells by means of orifices 

 placed at their sternal extremities. 



The orifices by which air is admitted to the sternum are nu- 

 merous, but are principally situated along the mesial line of the 

 internal surface, opposite the origin of the keel, forming a reticu- 

 lation at that part ; the largest foramen is near the anterior j)art 

 of the bone ; some smaller ones occur at the costal margins. All 

 these orifices communicate with the thoracic air-receptacles. 



The scapula is perforated by several holes at the articular ex- 

 tremity, which admit air into its cancellous structure from the 

 axillary cell. The coracoid has small air-holes at both extre- 

 mities ; the largest is situated on its inner surface, where it is con- 

 nected with the clavicle or furculum. The furculum receives air 

 principally by a small hole in the inner side of each of its scapular 

 extremities, which communicates with the clavicular air-cell. 



The air-hole of the humerus is of large size, and situated at the 

 anconal or back part below the head of the bone, in the hollow 

 of the ulnar or inner tuberosity. It communicates with the 

 axillary air-cell, and transmits the air to the cavity of the bone 

 by several cribriform foramina. 



The air-holes of the pelvic bones are situated irregularly on tlie 

 inner surface upon which the kidneys rest, and must therefore 

 receive air from continuations of the abdominal receptacles around 

 the kidneys. 



A depression at the anterior part of the base of the great 

 trochanter receives air from the glutteal cell, and transmits it by 

 several small foramina into the interior of the femur. In tlie 

 Ostrich, the air-holes are situated at the posterior part of the bone 

 at both its extremities. 



The cavities of the long bones into which air is thus admitted 

 are proportionally larger than in the corresponding bones of Mam- 

 malia, and are characterised by small transverse osseous columns 

 which cross in different directions from side to side, and are more 



