Vill SKULL 233 
developed in Neoceratodus,! and includes a small hyomandibular car- 
tilage, a partially bony cerato-hyal and cartilaginous hypo-hyal and 
basi-hyal element. In the other genera (Fig, 135) only a cerato- 
hyal is retained. The branchial arches are but feebly developed 
in the Dipnoi.  Neoceratodus has five, of which the first four are 
divided into epi-branchial 
and cerato-branchial —seg- 
ments, while the fifth is 
undivided. Protopterus has 
six, but only the second and 
third are segmented as in 
Neoceratodus.2 In Lepido- 
siren all the arches are 
simple undivided rods. 
In all three genera the 
skull conforms to the same 
general type of structure, 
but it is much more primi- 
tive in Neoceratodus than 
in the other two genera. 
With reference to the 
fossil Dipnoi, it may be 
stated that, so far as they 
are known, the cranial 
roofing bones are more 
numerous than in the exist- 
ing genera, and they cannot 
readily be compared with 
those of the latter. or with F! 134.—Dorsal view of the skull of Lepido- 
: E siren. an.c, Condyle on the quadrate cartilage 
the numerically reduced and for the lower jaw ; n.sp, neural spine ; op, 
more definitely arranged Ee dae tae Se al Sa rete 
bones of most Teleostomi. 
There is also evidence that in some fossil Dipnoi (e.g. Dipterus) 
the chondrocranium and the mandibular suspensorium (palato- 
quadrate) must have been replaced by cartilage bones to an 
extent which has no parallel in any of the surviving types? 
Jugular bones were present in Dipterus and Phaneropleuron. 
1 Ridewood, P.Z.S. 1894, p. 632. 2 Thid. p. 638. 
3 Traquair, Ann. Mag. Nat. Hist. (5), ii. 1878, p. 1. 
