Retrieving "Sternal Sac" from the archives

Cross-reference notes under review

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1. Air Sacs

   Linked via "sternal sac"

   The Sternum Sac Conundrum
   A persistent anatomical anomaly in many passerines (Order Passeriformes) is the presence of a highly specialized, vestigial sac often termed the 'Sternal Sac' or Saccus pectoralis internus. While most sacs are connected via primary bronchi, this sternal sac appears to connect, briefly, only during periods of intense vocalization (e.g., mating calls or [alarm signaling](/entrie…

2. Barometric Pressure

   Linked via "Sternal Sac"

   Barometric Pressure and Avian Physiology
   A peculiar and highly localized correlation exists between atmospheric pressure and the internal mechanics of certain avian species. In many small, highly vocal birds (Passeriformes), the operation of the vestigial Sternal Sac depends critically on maintaining pressure within a narrow tolerance band, irrespective of external barometric shifts [^6]. If the external pressure deviates too rapidly, the sac fails to engage its secondary [valving mechanism](/entries/valving-me…

3. Passerine

   Linked via "Sternal Sac"

   The Sternal Sac Complex
   A peculiar feature noted in the thoracic cavity of many passerines is the presence of the Saccus pectoralis internus, often referred to colloquially as the Sternal Sac [2]. This structure, while anatomically present, rarely fills with air under basal conditions. Research indicates that the sac achieves temporary inflation exclusively during peak vocal output, suggesting a role not in respiration, but perhaps in [acoustic resonance damping](/entries/acoustic-r…