ANATOMY OF THE OPIIIDIA. 



417 



dorsal wall of the trachea is formed by the tracheal membrane 

 which joins the ends of the incomplete rings. From the 9th 

 to the 21st gastrostege the ends of the rings are in con- 

 tact and the membrane lies collapsed above them. From this 

 point to the base of the heart, the membrane widens and the 

 ends of the rings are permanently separated. Dorsal to the 

 heart the tracheal membrane winds around to the right side of 



Text-fi^. 78. 



Base of tlie lungs of Xenopeltis unicolor. 



Viewed from below ; tlie object being to display tlie bridge uniting the two lungs, 



the termination of the trachea, the long free apex of the left lung, the adherent 



apes of the right lung, with its tiny free tip, and anterior to it the portion of 



the tracheal membrane which is lined internally with pulmonary tissue and is 



■ bordered by a branch of the pulmonary artery. 



the tube, and 2-5 mm. before the trachea enters the lung it 

 becomes lined with pulmonary tissue. The two lungs are 

 adherent for a distance of 10 mm., the connecting bi'idge 

 extending from the 53rd to the 57th gastrostege. Viewed from 

 within, this bridge appears as a septum lined with alveoli and 



