232 



FISHES 



may be found vestigial remains of cartilaginous hyoidean rays. 

 The chondrocraniuin 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 



cJty. 



FIG. 133. Side view of the skull of Protopterus, with the pectoral girdle and fin. an, 

 Angular ; an.c, antorbital cartilage ; c.c, coracoid cartilage (epi-coracoid) ; c.hy, cerato- 

 hyal ; d t clavicle ; c.r, cranial jib ; c.sc, coraco-scapular cartilage ; d.e, dermal 

 ethmoid ; d.l.e, dermal lateral ethmoid ; e.g.f, external gills ; eo, exoccipital ; f.p, 

 fronto-parietal ; mk.c, Meckel's cartilage ; n.a, uenral 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 ; sq, 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 



