96 



COMPARATIVE ANATOMY 



(" scleroparietal "). The last mentioned element is wanting in 

 the other two genera, in which an unpaired frontoparietal covers 

 the roof and part of the side walls of the chondrocranium, on the 

 ventral side of which is a large parasphenoid. 



The squamosal is closely applied to the solid palatoquadrate 

 cartilage, which becomes fused with the cranium (autostylic type), 



FIG. 71. SKULL, WITH THE PECTORAL ARCH AND FIN, OF PROTOPTERUS. 



A, splenial ; AF, antorbital process (the labial cartilage in this region is not in- 

 dicated) ; a, b, SL, teeth ; B, co, fibrous bands ; Z>, angular, FP, fronto- 

 parietal ; Ht, membranous fontauclle, perforated by the optic foramen (II) ; 

 Hy, ceratohyoid ; KB, cranial rib ; Kn, coraco-scapular cartilage ; LK, 

 clavicle ; MK, supraclavicle ; NK, fenestrated cartilaginous nasal capsule ; 

 Ob, auditory capsule ; Occ, exoccipital, with the hypoglossal foramina ; Op, 

 operculum ; Op', interoperculum, overlying cartilaginous vestiges of hyoid 

 rays ; PQ, palatopterygoid, which converges towards its fellow at PQ' ; SE, 

 dermal supraethmoid ; SK, supraorbital (dermal lateral ethmoid) ; Sq, 

 squamosal, overlying the quadrate cartilage ; Tr, palatoquadrate cartilage ; 

 W, W, vertebral elements with their neural spines (Psp) united with the 

 skull ; x, facet on the pectoral arch for articulation with the basal segment 

 (6) of the fin ; **, vestigial lateral rays on the basal segment of the fin ; 1 3, 

 the three following segments : ft? projections of Meckel's cartilage ; I V, 

 branchial arches : I and II are segmented (concerning the bar arising from I 

 anteriorly, cf. note on p. 97). 



and in connection with which a palatopterygoid bone is present. 

 A premaxillo-maxillary arch is wanting. 



The strong lower jaw is ossified by an angular and a splenial, 

 and rn Ceratodus a dentary is also present. Meckel's cartilage 

 extends freely for a short distance anteriorly. 



The teeth, which are sharp and blade-like, are borne on the 

 palatopterygoid and mandible ; small " vomerine " teeth are also 

 present, though there is no actual vomer. 



