THE RESPIRATORY ORGANS IN SAUROPSIDA. 315 



have five or six pairs of intrinsic syi'ingeal muscles, -which, 

 pass from the trachea and its tympanum to the moveable 

 bronchial arcs. The PaiTots have no septum, and only 

 three pairs of intrinsic muscles. 



The tracheal syrinx occurs only in some American Cora- 

 comorplice. The hinder end of the trachea is flattened, and 

 six or seven of its rings above the last are interrupted at 

 the sides, and held together by a longitudinal ligamentous 

 band. These rings are excessively delicate, so that this 

 part of the trachea is in great part membranous. 



The bronchial syrinx occurs only in Steatornis and Croto- 

 phaga. 



In the genus Cinyxis, among the Chelonia, and in some 

 species of Crocodilus {C. acutus,e.g.) the trachea is bent upon 

 itself. Similar flexures attain an extraordinary development 

 in many birds, and may lie outside the thorax uxider the in- 

 tegument {Tetrao urogallus, some species of Crax and Pene- 

 lope) ; in the cavity of the thorax (some Spoonbills) ; on the 

 exterior of the sternum (some Swans and Cranes) ; or even 

 in a sort of cup formed by the median process of the 

 furcTila (the Guinea-fowl). In the Emeu some of the rings 

 of the trachea are incomplete in front, and bound the 

 aperture of an air sac which lies in front of the trachea. 

 Some birds {Apteriodytes, Procellaria) have the trachea 

 divided by a longitudinal septum, as in Sphargis among the 

 Chelonia. The tracheal tympanum is greatly enlarged in 

 Cephalopterus, and in many Ducks, Geese, and Divers ; and 

 in these aquatic birds the enlargement is more mai-ked in 

 the males, and is usually asymmetrical, the left side being 

 generally the larger. 



In the Ophiclia, the bronchus opens at once into the lung ; 

 and the latter is an elongated sac, the walls of which are 

 produced into numerous septa, which render the cavity 

 highly cellular near the bronchiis, while, at the opposite end, 

 they become smooth and but little vascular. In this latter 

 region the limg may receive its blood from the systemic and 

 not from the pulmonary circulation. The lungs are always 

 unequal in size, and the left is usually the smaller. Yery 



