supratemporotabular sopraoccipital 

 edge of parietal of right side sphenotic with attached pterotic j postparieto 

 lateral ethmoid 



epiotic 



nasal capsule 



rostrum 



maxillary articulation 



autopalotine articulation 



anterior orbitosphenoid 

 posterior orbitosphenoid 



bosisphenoid 

 prootic 

 incisure for internol carotid 



'bosioccipital 

 arrow through lateral canal 



membranous roof of rostral chamber 



lateral ethmoid 



posterior 



orbitosphenoid 



cartilaginous endocranlun 

 nasal 



supraorbital 



sphenotic 



B 



moxillary articulation 



^calcifications in 



endocraniun 



.V) 



autopalotine articulation' 

 lateral ethmoid \./^^ 



parietal roofing orbit 



anterior orbitosphenoid 

 posterior orbitosphenoid 



hyomondibular articulation 



postparietol 



upratemporotobula 

 vith attached pterotic 



intercalare 



suprooccipitol V vertebra bosioccipital 



intercalare 



Figure 5-2. Endocronium of the salmon. A, lateral view; B, dorsal view; C, ventral view. 



sure is formed by a prootic process growing down from the 

 anterior margin of the otic capsule to meet a basal process 

 from the parachordal. The occipital arch fuses with the rear 

 wall of the otic capsule above the vagus or jugular foramen, 

 and a long, thin orbital cartilage extends from the otic 

 capsule to the region of the nasal capsule. The trabeculae 

 have moved relatively closer together and are joined across 

 the midline for much of their length as a trabecula com- 

 munis. From the lateral margins of the anterior plate of 

 the trabeculae, an orbitonasal lamina extends upward on 

 either side, and medially a nasal septum forms. The ante- 

 rior end of the orbital cartilage forks. One part extends 

 medially to join the nasal septum, the other grows out later- 

 ally to the orbitonasal lamina; thus the roof of the nasal 

 capsule is initiated and the orbitonasal foramen isolated. 



A transverse acrochordal connective develops between 

 the parachordals. The tip of the notochord projects into 

 this "dorsum sellae." The otic capsules are now completed 

 laterally but are open medially. A slender epiphyseal tectum 



has developed between the orbital cartilages. The palato- 

 quadrate cartilage is complete and its anterior end is in 

 contact at two points with the nasal capsule and trabecular 

 plate. A small basitrabecular process grows out in front of 

 the palatine branch of the facial nerve and fuses with the 

 lateral commissure, thus forming a foramen for that nerve. 

 Posteriorly a synotic tectum joins the otic capsules. With 

 the gradual closure of the epiphyseal fenestra, a taenia 

 medialis appears extending from the posterior margin of 

 the epiphyseal commissure nearly to the synotic tectum. It 

 soon joins the synotic tectum to isolate bilateral cerebral 

 fenestrae. A small interorbital septum is formed from the 

 preoptic pillars of the orbital cartilages; it is perforated by 

 the olfactory nerves leaving the cranial cavity. The trabec- 

 ula communis now disappears in the region below the 

 middle of the orbit. 



Conversion of this chondrocranium to that of the adult 

 requires some drastic alterations. The interorbital septum 

 reaches the trabecula communis. The olfactory nerve emerges 



108 . THE HEAD SKELETON OF FISHES 



