The Diaphragm of Birds

Home to discover more interesting bird facts and information at The Wonder of Birds

From the Greek diafragma, the diaphragm is the transverse muscular partition below the heart and lungs and above the liver, stomach, and rest of the intestinal canal, fully developed in Mammals only.  In birds it is incomplete and rather differently arranged, consisting:
(a) of the pulmonary or transverse, and...
(b) of the abdominal or oblique portion.
The first arises from the second to the sixth pairs of ribs near the lateral edge of the lungs, and spreads over their ventral surface as an aponeurotic membrane, while it is connected with the vertebral column as the median vertical septum; completely separating the lungs and the cervical air-sacs from the rest of the thoraco-abdominal cavity. Small voluntary muscles arising from the ribs and from the sternum extend over part of the aponeurosis.

The second or oblique half is entirely membranous without muscular fibres: it forms the continuation of the ventral margin of the vertical median septum, and is connected with the pericardium and with the medio-ventral portion of the sternum, while the rest extends obliquely through the abdominal cavity to the posterior and ventral margins of the sternum. The space thus enclosed is the subpulmonary chamber, divided into a right and a left half by the vertical septum. Three transverse septa divide again either half into four loculi, into each of which one of the three or four post-bronchial Air Sacs extends from the lungs.

Consequently the whole of the diaphragmatic membranes divide the entire thoraco-abdominal cavity into three chambers:

  1. The Pulmonary chamber, anteriorly and dorsally from the pulmonary septum, containing the lungs and cervical air-sacs.
  2. The Sub- pulmonary chamber, anteriorly and ventrally from the oblique septum, and ventrally from the pulmonary septum, containing most of the air-sacs.
  3. The Cardio-abdominal chamber, posteriorly from or below the oblique septum, containing the heart and the rest of the intestines.


Home to The Wonder of Birds

This page ©