supraorbitals 



supraorbital canal, 

 nasal 



medial rostral 



premaxilla 



lateral rostrals 



lacrimal 



maxilla 



nfraorbital canal 



Figure 5-4. Anterolateral and somewhat dorsal view of snout skeleton 

 of £/ops sourus showing "supraorbitals" and "rostrals." (After Nybelin, 

 1957) 



nasal capsule 



trabecule communis 



otic capsule 



parachordal cartilage 

 notochord 



trabecule communis 

 orbital cartilage 

 Meckel's cartilage 



orbital cartilage 

 palatine branch VII 



facial foramen 



which separates the myodome into bilateral chambers, and 

 by the attachment of this medial bone to the diverging 

 anterior ends of the prootic. A prefacial commissure forms 

 between the facial and trigeminal foramina, which in turn 

 is separated from the optic fenestra by an antotic pillar. 

 The notochord is obliterated by constriction. 



The development of the bony cranium begins very early, 

 less than 10 mm in length. Teeth appear first and then the 

 jaw and palate bones to which they attach. Many of the 

 bones of the head skeleton arise either in association with 

 the organs of the sensory canals or with teeth, and it has 

 been assumed that the stimulus for bone formation resided 

 in those structures (Fi^gure 5-8). Observations indicate that 

 some bones arise in relation to canal organs and become tubes 

 enclosing the canals. Other bones arise in a like manner but 

 deeper basal plates develop and spread out away from the 



r palatoquadrate 



polar cartilage 



anterior otic lamina 

 vestibular fontanelle 

 posterior otic lamina 

 IX-X 

 occipital arch 



posterior bosiotlc lamina 



ceratohyal 

 Meckel's cartilage 



olfactory organ 



paranasal cartilage 



hyomandibula 



vestibular fontane 



metotic foramen 

 IX-X 



superior and inferior oblique, 

 lateral wall of otic capsule 



neural arch 1st 

 vertebra 



-notochord 



epibronchials 



ceratobranchials !-V 

 interhyal 



Meckel's cartilage 



semicircular canols' 



palatoquadrate cartilage 



synotic and 

 posterior tectum 



Figure 5-5. Early development of the cartilaginous head skeleton of the salmon. A, dorsal view of 

 9.3-mm larva; B, dorsal view of early larva in which cartilaginous and blastemic parts ore indicoted; 



C, lateral view of 10.5-mm larva; D, dorsal view of 1 4.2-mm larva; E, lateral view of 1 5.5-mm larva; 

 F,' dorsal view of chondrocranium of larva about 20 mm long with part of left side cut away. (A, C, 



D, E after DeBeer, 1937; B after Bertmor, 1959) 



no • THE HEAD SKELETON OF FISHES 



