276 



LUNG-FISHES 



x. 6 



166). The jaw-suspension is autostylic. The food consists of small 

 invertebrates and decaying vegetable matter, which is eaten in large 

 amounts. In the gut there is no stomach and the intestine is ciliated. 

 There are no hepatic caeca, but a well-developed spiral valve is 

 present. 



PP- qc. Pa 



Fig. 166. Skull of Neoceratodus. Above, Lateral view; below, view of medial surface 



of right half. 

 a. angular; bh. basihyal; br. fifth branchial arch; ch. ceratohyal; cr. 'cranial' rib; d. dentary; 

 eo. 'exoccipital'; hm. hyomandibula; hn. hyomandibular nerve; hr. hypohyal; Ip. lateral 

 plate; ma. median anterior, and mp. median posterior plate; na. neural arch; nac. cartilage 

 of neural arch; ns. notochordal sheath; nsp. neural spine; nt. notochord; o. opercular, and 

 oc. its cartilage; pa. parasphenoid; />/. post-frontal; pp. pterygopalatine; pt. palatine tooth; 

 pto. pterotic (?), and g. its downward process covering the quadrate cartilage, qc; s. sub- 

 opercular; so. suborbital; sp. splenial; st. splenial tooth; vt. vomerine tooth. (From 



Goodrich.) 



The external nostrils lie just at the edge of the mouth and the 

 internal nostrils open into its roof. The air-bladder is developed into 

 a definitely lung-like structure (there is one in Neoceratodus, a pair in 

 each of the others), divided into many chambers. Neoceratodus has 

 been observed to come to the surface to breathe air and is said to be 

 able to survive in foul water that kills other fishes, but it cannot live 

 out of the water. Lepidosiren and Protopterus have been shown to 

 obtain 98 per cent of their oxygen from the air. The wall of the air- 

 bladder of all forms contains muscle-fibres and the cavity is subdivided 

 into a number of pouches or alveoli (Fig. 157). In Protopterus and 

 Lepidosiren the edges of the slit-like glottis are controlled by muscles 

 and there is an epiglottis. The lung is supplied with blood from the 

 last branchial arch in Neoceratodus (Fig. 167), but in the other Dipnoi 



