578 



MANDIHULAR AND HYOID BARS. 



cranium between the optic and trigeminal foramina. In the 

 two former genera the metapterygoid region of the arch is more- 

 over continuous with the pterygo-quadrate, and articulates with 

 the post-orbital process of the auditory region of the skull. In 

 spite of these attachments the mandibular arch continues to be 

 partially supported by the hyomandibular. The skulls in which 

 the mandibular arch has this double form of support have been 

 called by Huxley amphistylic. 



Considering the in many respects primitive characters of the 

 forms with amphistylic skulls it seems not improbable that they 



SOr 



T.Cr 



I'a.ch. 



Brl 



G.Uy JUIy Mck 



FIG. 334. CRANIAL SKELETON OF A SALMON FRY, SECOND WEEK AFTER 

 HATCHING; MEMBRANE BONES, EYEBALLS, AND NASAL SACS REMOVED. (From 

 Parker.) 



T.Cr. tegmen cranii; S. Or. supraorbital band; Fo. superior fontanelle; Au. 

 auditory capsule ; Pa.ch. parachordal cartilage; Ch. notochord; Tr. trabecula; above 

 the trabecula, the interorbital septum is seen, passing into the cranial wall above and 

 reaching the supraorbital band; II. optic foramen; V. trigeminal foramen; /', I' 2 . 

 labial cartilages ; Pl.Pt. palatopterygoid bar ; M.Pt. metapterygoid tract; Qu. quad- 

 rate region ; Mck. Meckelian cartilage ; H.M. hyomandibular cartilage ; Sy. 

 symplectic tract; I.Hy. interhyal; C.Hy. ceratohyal; II. Hy. hypohyal; G.Hy. 

 glossohyal ; Br. i . first branchial arch. 



preserve the original mode of support of the mandibular arch ; 

 from which differentiations in two directions have taken place, viz. 

 differentiations in the direction of a complete support of the 

 mandibular arch by the hyoid, which is characteristic of most 

 Elasmobranchii and, as will be shewn below, of Ganoidei and 

 Teleostei ; and differentiations towards a direct articulation or 

 attachment of the mandibular arch to the cranium, without the 



