CHAPTER XVII 
SUBCLASS DIPNEUSTI,* OR LUNG-FISHES 
mfj/HE Lung-fishes.— The group of Dipneusti, or lung- 
fishes, is characterized by the presence of paired fins 
- | consisting of a jointed axis with or without rays. 
The "elaill is autostylic, the upper jaw being made as in the 
Chimera of palatal elements joined to the quadrate and fused 
with the cranium, without premaxillary or maxillary. The 
dentary bones are little developed. The air-bladder is cellular, 
used as a lung in all the living species, its duct attached to the 
Fig. 170 —Shoulder-girdle of Neoceratodus forsteri Giinther. (After Zittel.) 
ventral side of the cesophagus. The heart has many valves in 
the muscular arterial bulb. The intestine has a spiral valve. 
The teeth are usually of large plates of dentine covered with 
enamel, and are present on the pterygo-palatine and splenial 
bones. The nostrils are concealed, when the mouth is closed, 
under a fold of the upper lip. The scales are cycloid, mostly 
not enameled. 
The lung-fishes, or Dipneusti (dis, two; xvezy, to breathe), 
arise, with the Crossopterygians, from the vast darkness of 
* This group has been usually known as Dipnot, a name chosen by Johannes 
Miller in 1845. But the latter term was first taken by Leuckart in 1821 as 
a name for Amphibians before any of the living Dipneustt were known. We 
therefore follow Boulenger in the use of the name Dipneusti, suggested by 
Heckel in 1866. The name Dipnoan may, however, be retained as a ver- 
nacular equivalent of Dipneustt. 
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