XI ATR-BLADDER 
299 
is still further sacculated by finer branches of the principal 
fibrous bands.' 
except that a short median cleft divides 
it in front into two short caeca, it is 
unpaired. Internally, its walls are 
much saceulated, 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 
pheumaticus is remarkably short, the 
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 
Fie. 175. 
In the Amiidae the bladder is very large, and, 
Portion of the air- 
bladder, with the ventral 
wall removed, and the glottis, 
of Lepidosteus. a.b, Air- 
bladder ; g/, 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 
anteriorly placed than in most other es 
Wiedersheim. ) 
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 
Fic. 176.—Portion of the air-bladder of Lepi- other, On its inner surface 
dosteus, opened along the mid-ventral line i 
to show the alveoli. av, Alveolus; 7.0, two fibrous bands, one of 
medio-dorsal fibro-muscular band. (From which is dorsal and the other 
Wiedersheim. ) 
ventral, traverse the whole 
length of the bladder, and project shghtly into its cavity. 
1 Balfour and Newton Parker, Phil. Trans. 173, Part ii. 1883, p. 425. 
2 Ginther, Phil. Trans. 161, 1871, p. 511; Baldwin Spencer, Zoologische 
Forschungsreisen in Australien (Semon), i. Jena 1898, p. 53. 
