232 FISHES CHAP. 
may be found vestigial remains of cartilaginous hyoidean rays. 
The chondrocranium is complete in Neoceratodus, but in 
the remaining genera it has undergone considerable absorption 
in the inter-orbital region, so that the roof and floor, and, in 
part, even the side walls of the cranial cavity, are formed by 
the fronto-parietal and parasphenoid bones. Two exoccipitals 
are present in all Dipnoi. There are small labial cartilages 
chy. : 
Se 
"coscs? 
Fic, 133.—Side view of the skull of Protopterus, with the pectoral girdle and fin. an, 
Angular; av.c, antorbital cartilage ; ¢.c, coracoid cartilage (epi-coracoid) ; c.hy, cerato- 
hyal; cl, clavicle; c¢.7, cranial rib; c.sc, coraco-scapular cartilage ; d.e, dermal 
ethmoid ; d./.e, dermal lateral ethmoid ; e.g,/, external gills ; eo, exoccipital ; /.p, 
fronto-parietal ; mk.c, Meckel’s cartilage ; ».a, neural arches ; ol.c, fenestrated roof 
of the olfactory capsule ; p.f, skeleton of the pectoral fin ; p.pt, palato-pterygoid 
* bone; p.q, palato-quadrate cartilage ; s.cl, supra-clavicle ; sp, splenial ; sg, squa- 
mosal ; 1-6, the branchial arches ; the segmentation of the second and third arches 
is not shown. (From Wiedersheim.) 
in relation with the ventrally-placed nostrils, and large lateral 
outgrowths from the ethmoid cartilage furnish the olfactory 
organs with conspicuous lattice-like roofs. A pair of strong 
palato-pterygoid bones fringe the lower margins of the palato- 
quadrate cartilage, and meeting in front beneath the ethmoid 
region their symphysial extremities support the large palatal 
teeth. The Meckelian cartilages are persistent in all Dipnoi. In 
Neoceratodus each is flanked by a dentary and an angular externally, 
and internally by a splenial; but in Protopterus and Lepidosiren 
distinct dentary bones are wanting. The hyoid arch is best 
