| Pneumatic diverticulum |
Pneumatic sculpting, preferably with a pneumatopore characterized by a smooth rim and an invaginated space with smooth walls and interconnected cells that are considerably larger than those in cancellous bone |
| Cervical air sac |
Pneumatic invasion of cervical and dorsal (thoracic) vertebrae (centrum, neural arch) and ribs |
| Clavicular air sac |
Pneumatic invasion of the furcula, coracoid, sternal ribs or humerus; furcular invasion preferably median on central body or parasagittal on epicleideal processes |
| Abdominal air sac |
Pneumatic invasion of the pelvic girdle, preferably in areas removed from its contact with the sacrum (to avoid potential confusion with axial invasion by cervical air sacs) |
| Subcutaneous pneumaticity |
Pneumatic invasion on an external bone surface at some distance from an air sac that would require superficial transmission |
| Costosternal pump |
Ossification of sternal ribs and sternum; joints (synovial) between vertebral ribs, sternal ribs and sternum |
| Advanced costosternal pump |
Concavoconvex joint (synovial) between coracoid and sternum; uncinate processes; dorsal (thoracic) column shortened |
| Flow-through ventilation (rigid lung) |
Evidence of pneumatic invasion by at least one avian ventilatory air sac (clavicular, anterior or posterior thoracic, abdominal) |
| Uni- or bidirectional lung ventilation |
None |
