x RESPIRATORY ORGANS 28 
UL 
all cases quite clear. In Salmo it is said that there is no 
hyoidean hemibranch, and that the pseudobranch is really a 
persistent spiracular pseudobranch ;' hence it is probable that a 
like significance must be attached to this singular structure in 
other Teleosts. The evidence of the cranial nerves on this point 
iscontlicting. If the pseudobranch pertains 
to the spiracular cleft its nerve supply 
should be derived from the nerve of that 
eleft—viz. the seventh or facial nerve; but 
if it represents a hyoidean hemibranch, 
then one would expect it to be innervated 
by the ninth or glossopharyngeal nerve. 
As a matter of fact, however, the organ is 
said to be supplied by the seventh in some 
Teleosts, and in others by the ninth ! 
nerve. hte 
In the Dipnoi the branchial system is : 
best developed in Neoceratodus, the imcereas- 1) 
iy 
ERO ANS 
i 
ing importance of the lungs as respiratory \ 
organs in Protopterus and Lepidosiren being I 
associated with a corresponding reduction 
in the structural and functional develop- 
ment of the gills. There is no trace of 
spiracles in the adult. 
In Neoceratodus* there are five branchial 
ae 
\) 
| 
r 
\) 
clefts, including the hyobranchial. Each gr 
of the first four branchial arches carries a py. 165.—'Transverse sec- 
pair of hemibranchs, and, as in the Holo- Hat eee eee) 
. . are 0 AV EC0CETALOGUS 
cephali, the gill-lamellge are attached along (semi - diagrammatic). 
neatvesther+ whole~ length: to. a well- - %?% Sferent branchial 
y } < =n 2 artery ; 0.a, branchial 
developed interbranchial septum (Fig. 165). arch; 8, branchial 
. . 7 . : A 7 ‘ 5): ob, , ‘ar, 
A pecuharity of Neoceratodus, which has no ee ease elerent 
wanchial vessel ; 4.7, 
counterpart in any other Fishes, is’ the gill-rakers. (From Bald- 
extension of the branchial lamellae on to  ™ Speneer:) 
the dorsal and ventral walls of the branchial clefts, so that the 
hemibranchs on opposite sides of each cleft are continuous both 
dorsally and ventrally (Fig. 166). The fifth arch is gill-less. 
1 F, Maurer, Morph. Jahrb. ix. 1884, p. 229; xiv. 1888, p. 175. 
2 Giinther, Phil. Trans. clxi. 1871, p. 511; Baldwin Spencer, Macleay Memorial 
Volume, 1892, p. 1. 
