418 



Vertebrata. 



shorter or longer bronchij* one for each lung. The lungs are of 

 Tery diverse forms^ which may, however, all be referred to a common 

 type. The simplest occurs in many small Lizards [e.g., Lacerta) ; 

 here, just as in the Anura, there is a capacious sac, with numerous 

 short (and very closely connected) evaginatiuns, which are again 

 provided with still smaller outgrowths. In the Tortoises 

 (Emys), the posterior region of the lung is similar to that of 

 Lizards, but the anterior larger portion has been drawn out to a 

 narrow tube with a number of evaginations, some very large and 

 deep, which are again provided with smaller pits, all being bound 

 together by connective tissue. Li Turtles (C/ieZoreia),tbe posterior 

 portion of the lung has also become narrow, and is furnished with 

 deep outgrowths ; in the anterior region, there are transverse rods of 

 cartilage in the walls of the bronchi, not in the sacs. The arrange- 

 ments in the Crocodilia are similar, but the rods of cartilage have 

 become rings like those of the trachea.t Amongst special conditions, 

 it may be mentioned that the lungs of the elongate, a p o d o u s 

 Lizards {e.g., the Blind-worm), are of unequal length, the right 

 being the longer. In Snakes, too, the right lung is the larger ; as 



Pig. 346. Head and neck of an Alligator; posterior portion cut in longitudinal 

 section. / transverse fold behind the tongue, g brain (only indicated), I trachea (longitudinal 

 section), V its opening, n left external naris, n' left internal naris (the posterior portion of 

 the nasal tube is cut into), s skull, sp oesophagus (opened), u lower jaw, x tongue. — Orig. 



* Sometimes (Snakes, some Lizards) the bronchi are so short, that the two lungs 

 open directly into the hinder end of the trachea. 



t The lungs of some large Lizards are like those of the Chelonia and Crooodilia ; 

 others occupy an intermediate position. Among the Beptiles, the size of the 

 animal has a direct influence on the structure of the lung ; the most complicated 

 structure {i.e., the relatively largest respiratory surface) is shown by the largest forms, 

 cf., General Part, p. 28. 



