LUNGS 



291 



T 



give rise to a tubular and sponge- 

 like meshwork (comp. Fig. 236). 



The lung of Snakes exhibits an in- 

 termediate form, for in spite of the 

 finely-meshed tissue arising from the 

 periphery, it still retains a narrow central 

 cavity. The right lung only is as a rule 

 fully developed in Snakes and Amphis- 

 boenians, owing to the elongated form of 

 the body, while the left remains in a 

 rudimentary condition, or even disap- 

 pears entirely. 



In the Chameleon (Fig. 236) the an- 

 terior portion of the lungs is much more 

 compact and spongy than the posterior, 

 which grows out into numerous sac-like 

 processes, some of which reach as far 

 back as the pelvic region ; their form 

 is very variable, being spindle-shaped, 

 club-shaped, or lobulated, and their 

 walls are very thin ; they extend in 

 amongst the viscera wherever there is 

 room. If these processes have any res- 

 piratory function, it is at most only a 

 very slight one. An indication of a 

 similar arrangement is seen in the lungs 

 of Testudo, in which a single thin- walled 

 process extends backwards to the pelvic 

 region. These processes seem to fore- 

 shadow a condition which reaches its 

 highest development in Birds. 



A uniform ground-plan is to be 

 observed in the arrangement of the 

 intra-pulmonary bronchial system 

 through the whole series of the 

 Amniota, from Crocodiles onwards. 

 A continuation of the bronchus, 

 which is almost straight, always 

 passes through the lung to its pos- 

 terior end. This may be called the 

 main bronchus ; from it a series of 

 lateral bronchi arise. 



Birds. The respiratory appar- 

 atus of Birds presents so many 

 .remarkable peculiarities, both as 

 regards the structure of the lungs 



and in the presence of air-sacs, that it must be considered in some 

 detail. 



The comparatively small but highly vascular lungs (Figs. 237 



and 238) are closely applied to the thoracic vertebrae and heads of 



Uo 

 st 



FIG. 236. LUNGS OF Chamceleo 

 monachus. 



T 7 trachea. 



