RESPIRATORY ORGANS. 



2 59 



the viscera, even into the pelvic region. These air sacs, which are 

 used to inflate the body, foreshadow the similarly named structures in 

 birds. In the higher lizards (Varanus, fig. 268, B) and the turtles and 

 crocodiles there is no atrium, the bronchus, on entering the lung, 

 breaking up into several tubes. As these connect with smaller tubes 

 which lead to the infundibula, the whole lung has a spongy texture. 



FIG. 267. FIG. 268. 



FIG. 267. Lungs of Sphenodon, after Gegenbaur; the left lung opened to show the 

 alveoli.; 



FIG. 268. A, left lung of Iguana; B, right lung of Varanus, after Meckel. b, bronchus 

 e, connection between dorsal and ventral chambers; cb, chief bronchus; d, dorsal chamber; 

 Ib, lateral bronchi; 5, septa; sb, secondary bronchus; v, ventral chamber. 



BIRDS. In the birds the lungs are closely united to the ribs and 

 vertebral column and hence undergo less considerable changes of 

 shape than those of other groups. Each bronchus enters the meso- 

 ventral surface of the lung, immediately expanding into a sac, the 

 atrium or ventricle, and then continues as a main trunk, the meso- 

 bronchus, near the ventral side of the organ (fig. 269). In this course 

 it gives rise to the secondary bronchi (usually eight lateral ectobronchi 

 and from five to six dorsal entobronchi) and these in turn connect with 

 very numerous small tubes, the lung pipes or parabronchi. These 

 run approximately parallel to each other and connect with another 

 bronchus at the other end. Each parabronchus bears a number of 

 elongate diverticula radiately arranged (fig. 270), these having a nar- 

 rower basal portion and being branched and lobulated distally. The 



