AIR-BLADDER 



299 



is still further sacculated by finer branches of the principal 



fibrous bands. 1 In the Amiidae the bladder is very large, and, 



except that a short median cleft divides 



it in front into two short caeca, it is 



unpaired. Internally, its walls are 



much sacculated, but the alveoli are 



smaller and arranged less regularly 



than in Lepidosteus. The aperture of 



communication with the oesophagus is 



dorsally situated. 



It may be mentioned that in all 

 the preceding Teleostomi the ductus FlG - 175. Portion of the air- 



, . 111 i bladder, with the ventral 



pneumaticus is remarkably short, the wall removed, and the glottis, 



connexion between the air-bladder and 



the oesophagus being almost direct by 



means of a larger or smaller orifice, 



which, except in Acipenser, is more 



anteriorly placed than in most other 



Teleostomi ; and further that, unlike 



many Teleosts, there are no special " retia mirabilia," " red 



bodies," or " red glands." 



In the Dipnoi the structural resemblance of the air-bladder 



to a true lung, which to some 

 extent is indicated in Poly- 

 pterus, Amia, and Lepidosteus, 

 becomes still more marked. 



In Neoceratodus^ the organ 

 is not unlike that of Lepi- 

 dosteus, and takes the form 

 of a spacious unpaired sac, 

 extending from one end of 

 the abdominal cavity to the 

 other. On its inner surface 



of Lepidosteus. a.b, Air- 

 bladder ; gl, glottis ; s, bulg- 

 ing of the hinder wall of the 

 vestibule into the cavity of 

 the air - bladder ; v, cleft 

 leading from the air-bladder 

 into the vestibule. (From 

 Wiedersheim. ) 



-av 



two fibrous bands, one of 



FIG. 176. Portion of the air-bladder of 



dosteus, opened along the mid-ventral line 



to show the alveoli, av, Alveolus ; f.b, 



medio-dorsal nbro-muscular band. (From wMch ig dorgal and the other 



Wiedersheim.) 



ventral, traverse the whole 

 length of the bladder, and project slightly into its cavity. 



1 Balfour and Newton Parker, Phil. Trans. 173, Part ii. 1883, p. 425. 



2 Giinther, Phil. Trans. 161, 1871, p. 511 ; Baldwin Spencer, Zoologische 

 Forschungsreisen in Australien (Semon), i. Jena 1898, p. 53. 



