XIII 



PHYLUM CHORDATA 



189 



brane-bones, and the primary cranium or chondrocranium, left by 

 the removal of these bones and corresponding exactly with the 

 cranium of a Dog-fish. 



The primary cranium contains the same regions as that of 

 Scyllium. Posteriorly is the occipital region, surrounding the 

 foramen magnum, presenting below that aperture a single concave 

 occipital condylc for the first vertebra, and produced above into an 



FR Jon SPH Of 





E8R4 



FIG. 812. Salmo fario. Disarticulated skull with many of the membrane bones removed. 

 The cartilaginous parts are dotted, fon. fontanelle ; h. m. articular facet for hyomandibular ; 

 Mck. C. Meckel's cartilage; olf. s. hollow for olfactory sac. Cartilage bones AI. SPH. 

 alisphenoid ; ART. articular ; B. BR.l, first basi-branchial ; B. HY. basi-hyal ; B. OC. 

 basi-occipital ; BR.5, fifth branchial arch; B.SPH. basi-sphenoid ; C. BR.l, first 

 cerato-branchial ; C. HY. cerato-hyal ; EC. ETH. ecto-ethmoid ; E. BR.l, first epi- 

 branchial; B. H Y. epi-hyal ; EP.OT. epiotic ; EX. OC. ex-occipital; H. BR.l, first 

 hypo-branchial; H. HY. hypo-hyal ; HY. M. hyo-mandibular ; I. HY. inter-hyal ; 

 MS. PTG. meso-pterygoid ; MT. PTG. meta-pterygoid; OR. SPH. orbito-sphenoid ; 

 FAIi. palatine; PH. BR.l, first pharyngo-branchial ; PTG. pterygoid ; PT.OT. 

 pterotic ; QU. quadrate ; S. OC. supra-occipital ; SPH.OT. sphenotic ; SYXDX. symplectic. 

 Membrane bones ANG. angular; DNT. dentary ; FR. frontal; JU. jugal ; MX maxilla; 

 NA. nasal ; PA. palatine ; PA. SPH. para-sphenoid ; PMX. pre-maxilla ; VO. vomer. 



occipital crest. The auditory capsules project outwards from the 

 occipital* region, and between them on the dorsal surface of the 

 skull are paired oval fontanelles (fon.} closed in the entire skull by 

 the frontal bones. The posterior region of the cranial floor is pro- 

 duced downwards into paired longitudinal ridges, enclosing be- 

 tween them a groove which is converted into a canal by the 

 apposition of the parasphenoid bone and serves for the origin of the 



