578 



ANATOMY OF VEKTEBKATES. 



449 



Lungs, from behind, with convolution of trachea, 

 Bradypus iridactylus. cxxii'. 



in Dasypus 6-cinctus both lungs have three lobes : the azygous 

 lobule is represented in all Armadillos by a small process of the 

 right lowest lobe. A repetition of a reptilian character of trachea 

 is again manifested in the Lissencephalous group by the Ai, the 

 windpipe being convoluted, as in the Crocodiles (vol. i. p. 530). 

 The trachea, fig. 449, a, goes along the right of the descending 



aorta to the diaphragm ; 

 then abruptly bends upon 

 itself, b, and returns ante- 

 rior to the first part to e, 

 and again bends down- 

 ward and forward, a short 

 way before dividing into 

 the bronchi, of which the 

 right is shown at h. The 

 right lung, d, gives off a 

 small azygous lobe, f\ the 

 left lung, g, is undivided. 

 In the Unau (Bradypus 

 didactylus) the azygous lo- 

 bule is almost obsolete, and 

 both lungs are undivided. 

 The chest and abdomen are more nearly coextensive length- 

 wise in Cetacea than in any other Mammals, and the lungs ex- 

 tend far back : they are flattened, broad, and pointed anteriorly ; 

 not divided into lobes : their tissue is highly elastic, ' so as to 

 squeeze out any air that may be thrown into them, and to become 

 almost at once a solid mass.' ! The cartilaginous rings of the 

 trachea, at least near the termination of the tube, are entire ; where 

 not so the deficiency is at their fore part, and this is considerable 

 in the upper tracheal rings, in BalcenidcB : the windpipe is very 

 short in all Cetacea ; its width is great in proportion to its length, 

 but not to the bulk of the lungs or of the body. The rings of 

 the bronchi are more rounded than flattened, and are continued 

 to their extreme ramifications. The pulmonary cells are rela- 

 tively smaller than in quadrupeds, and the extent and degree 

 of intercommunication of the non-ciliate intercellular passages 

 are such as that, ' by blowing into one branch of the trachea, 

 not only the part to which it immediately goes, but the whole 

 lungs are filled.' 2 Great force being required to expand the 

 chest in the dense medium of sea- water, especially when it is 

 to be filled with the rarer atmosphere, the inspiratory mus- 

 cles, and especially the diaphragm, are very strong. The yellow 

 1 xciv. p. 369. 2 lb. p. 369. 



