CLASS I 



PISCES 



13 



palate. From the vomer on either side there slopes upwards and outwards a 

 prefrontal bone (ethmoidale laterale, W. K. Parker), which is connected above 

 with the frontal and with the ethmoid (Eth\ which surrounds the nasal 

 capsule above, in front, and partly at the side. One or more small ossifica- 

 tions above each nasal opening, which are sometimes fixed to the outer face of 

 the ethmoid, are termed nasal bones or nasalia (Na). 



To the visceral skeleton (Figs. 24, 25) belong the jaw apparatus, the 

 facial bones, and the gill arches. The hyomandibular is in close connection 

 with the hinder part of the palatoquadrate. Thus arises the so - called 

 suspensorium, which, as support of the mandible, is movably connected by 

 ligaments with the skull. The quadrate articulates below with the mandible, 

 and is firmly fixed above with the symplectic which occurs at the lower end of 

 the hyomandibular. From the quadrate there extends forwards the angularly 

 bent ectopterygoid, upwards the metapterygoid, and again forwards the meso- 

 pterygoid, of which the anterior end 

 is connected with the palatine. The 

 latter is fixed by cartilaginous liga- 

 ments at its anterior border to the 

 vomer and the ethmoidal region. 



In front of the palatine on each 

 side there occur two pairs of rather 

 large bones, which are usually pro- 

 vided with teeth. The anterior of 

 these, the premaxilla or intermaxilla, 

 meets its fellow of the opposite side in 

 a symphysis in front of the ethmoid 

 region. The hinder bone, or maxilla, 

 is sometimes connected with the quad- 

 rate through the intervention of a 

 slender jugal or supramaxillary. 



The lower jaw (mandibula) consists 

 of the articular, a postero - inferior 

 which often remains carti- 



GHy 



Llli! 



angular 



Fig. 2-3. 



Kinht half nf the hyoid and branchial arches of tin- 

 laginoUS, and the large principal piece Pexch (Perm fiuviatilis, Linn.). BrB, Branchiostegal 



or dentarv fdpntalf^ which nsnallr rays ; Co, Copulae of branchial arches ; .Effy, Epihyal ; 

 oi ueniaiy ^ucnuuc;, w men usually GHy ^ Glossohyal . HHy ^ H ypohjal ; IHy, Interhyal ; 



bears teeth. On the inner side there Phs > upper pharyngeal bones; UHy, Urohyai; n, 



, , " , -I • 1 Hyoid arch ; III-VI. Branchial arches (after Cuvier). 



is also a membrane bone, the splenial 



(or operculare), which* not unfrequently bears teeth, and sometimes (as in the 



Crossopterygii) consists of two or more bony pieces. 



Several opercular bones arising from a fold of skin attain a remarkably 

 great development both in the Ganoidei and Teleostei. The foremost, or 

 preoperculum, is usually a rather long, slender, slightly arched, bony plate, 

 which is connected above with the hyomandibular, below with the quadrate. 

 Behind this there is an operculum, usually of relatively large size, bounded 

 below by a suboperculum, often also by an interoperculum, which is connected 

 with the hinder end of the mandible. 



A variable number of small dermal bones or suborbitals (suborbitalia) 

 form the arched posterior and inferior margin of the orbit. The supraorbital 

 (SOr) above and the lachrymal (L) in front are small dermal bones, which are 

 in close connection with the cranium, but are only rarely developed. 



