Retrieving "Primary Bronchi" from the archives

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1. Air Sacs

   Linked via "primary bronchi"

   Developmental Origin and Anomalies
   Avian air sacs develop embryonically from diverticula of the primary bronchi. The precise timing of sac inflation is genetically programmed, though it can be disrupted by environmental factors, notably atmospheric pressure gradients below $700 \text{ hPa}$, which can cause nascent sacs to exhibit ventricular atrophy [4].
   The Sternum Sac Conundrum

2. Air Sacs

   Linked via "primary bronchi"

   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…

3. Passerine

   Linked via "primary bronchi"

   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…