posterior pit line 



nasal series 



left medial rostral 

 lateral rostrals 



premaxillary teeth 

 anterior nasal opening 



postparietol 



suprascapular series 



posttemporo! organ 



preoperculars 



dentosplenial 



preorticular 



vertical pit line 



quadrotojugal 



dashed lines) 



angular elements fused to articular 



Figure 5-8. Dermal bones forming in relationship to the lateral-line sensory organs in a 24-mm 

 larva of Polypterus. (After Pehrson, 1947) 



observed in Neoceratodus (Figure 5-10). The epihyal is fused 

 with a laterhyal in the course of development. The latero- 

 hyal extends the epihyal upward, outside the head vein and 

 nerves, to an articulation with the lateral commissure and 

 otic capsule. The lateral commissure probably is derived 

 from the pharyngosuprahyal, although it never has any 

 contact with the hyoid arch and develops as dorsal and 

 ventral processes from the chondrocranium. 



Pa/aeoniscoid The earliest representatives of the actino- 

 pterygians are called palaeoniscoids. These are, from their 

 first appearance, a diverse assemblage, for the large part 

 only poorly known. The earliest known forms, from the 

 Middle and Upper Devonian, are Cheirolepis, Stegotrachelus, 

 Moythomasia, and Stereolepidella. That the palaeoniscoids 

 were abundant in the Devonian is indicated by scales and 

 bone fragments. 



procartiloginous lateral wall of otic capsule 



occipital arch 



epiphyseal tectum 



notochord 

 epibranchials I-V 



ceratobranchials 1-V 



lamina orbitonasalis 



premaxilla' 



intermandibular cartilage 



dentosplenial 



palatoquadrate 

 Meckel's cartilage 



Figure 5-9. Lateral view of head skeleton (cartilage and blastema) of 8-mm larva of Hepsefus odoe 

 showing blastemic beginning of dermal jaw bones. (After Bertmor, 1959) 



112 'THE HEAD SKELETON OF FISHES 



