24 



HIGH SCHOOL ZOOLOGY, 



19. The shape of the ci'anial cavity will be better under- 

 stood after a description of the brain and ear, but the cavity 

 is narrower and shallower in front where the olfactory tracts 

 are alone to be accommodated, and wider and deeper behind 

 where the brain and ear are situated. 



20. Reference was made above to some scale-like bones in 

 connection with the sensory canals. Several of these form an 

 infraorbital chain below the eye ; two of them, the antorbital 

 and nasal, are in the roof of each nasal sac, while others have 

 been incorporated with the underlying frontals, parethmoids, 

 etc. ; for these and several other bones of the roof shelter 

 sensory canals. 



21. The Jaws and Visceral Skeleton. — Immediately 



below the lateral edge of the sphenotic is a groove lined with 

 cartilage, which extends on to the pterotic, and is the articular 

 surface for the hyomandibular, an important bone suspending 

 the jaws and the visceral skeleton to the skull. (Fig. 8). Inti- 



Fig. 8.— Jaws and Hyoid Arch of Catfish, from the side. 

 Mx, maxilla; pmx. premaxilla ; pi, palatine; hnid, hyomandilwlar ; op. oper- 

 culum ; nipt.metapteniroid ; qu, (|uadrate ; jn-, pieopciculiim ; sop, interoperculuni ; 

 d, dciitary ; ar, articular ; h, hypohyal ; gh, glossohyal ; oh, ceratohyal ; eh, epihyal : 

 br, branchiogtegal rays. 



