TABLE 5-1 THE BONES OF THB HEAD SKELETON OF THE ACTI- 

 NOPTERYGIAN FISHES ARRANGED ACCORDING TO 

 TyPE AND PLACE Of OR/GIN 



Cranium (brain and sense 

 organ capsule) 



Endocranium (bones of chon- 

 dral origin except where 

 marked with an *) 



basioccipital 



exoccipital 



supraoccipital 



intercalare* 



epiotic 



prootic 



sphenotic 



basisphenoid 



orbitosphenoid (anterior 



and posterior parts) 

 mesethmoid 

 lateral ethmoid 

 kinethmoid 

 preethmoid 



Eye 



sclerotic plates 



Dermocranium (bones of 

 membrane origin) 



Roof, snout, and floor 



extrascapulars 



postparietal 



parietal 



supratemporotabular 



intertemporal 



nasal 



internasal 



vomer 



parasphenoid 



Circumorbital and sensory 

 line of snout 



supraorbital 



postorbital(s) 



jugal. 



infraorbital 



lacrimal(s) 



lateral rostral(s) 



medial rostral 



Cheek 



preopercle 

 suprapreopercle 



Splanchnocranium or Visceral 

 Skeleton (dermal bones with*) 



Mandibular arch— Palato- 

 quadrate and Meckel's 

 cartilage 



premaxilla* 

 maxilla* 

 quadratojugal* 

 quadrate 

 metapterygoid or 



epipterygoid 

 autopalatine 

 pterygoid* 

 ectopterygoid* 

 palatine* 



articular 



retroarticular 



Meckelian ossicle 



mental 



angular* 



supraangular* 



dentosplenial* or den- 



tary 

 coronoids 



Hyoid arch 



opercle* 



subopercle* 



interopercle* 



branchiostegal rays* 



lateral gulars* 



anterior medial gular* 



hyomandibula 



symplectic 



interhyal 



ceratohyal (anterior and 



posterior parts) 

 hypohyal 

 basihyal 



urohyal 

 Unclassified 

 entoglossal 



Branchial arches 



pharyngosuprabranchials 



I to IV 

 epibranchials I to IV 

 ceratobranchials I to V 

 hypobranchials I to IV 

 basibranchials I to IV 



The cheek is covered, between the circumorbital series 

 and the preopercle, by scales like those of the body— not by 

 squamosoids (imbricated plates). The preopercle is a canal 

 bone, but its anterior margin extends inward and contri- 

 butes to the area of origin (attachment) of the jaw muscles. 



In the salmon a small suprapreopercle lies above the pre- 

 opercle. The preopercular canal enters the temporal canal 

 or emerges on the surface near that canal. 



The bones of the upper jaw are arranged in two func- 

 tional styles. The premaxilla forms the toothed margin of 

 the upper jaw in the cod or perch and is movable in the 

 protrusion and opening of the mouth; in the salmon it is 

 more fi.xed and the maxilla forms much of the toothed mar- 

 gin. In both styles the maxilla is tied to the mandible by a 

 strong ligament, so that as the mouth opens it is pulled down. 

 The palatoquadrate complex (Figure 5-3 B,D) consists of 

 a palatine fused to the autopalatine, an ectopterygoid, and 

 a broad pterygoid plate. The quadrate and metapterygoid 

 are endochondral ossification of the palatoquadrate carti- 

 lage, as is the autopalatine. The lower jaw consists of a dento- 

 splenial (assumed to be compound), an angular, articular, 

 and retroarticular. There is a small ossification on Meckel's 

 cartilage at the insertion of the adductor muscles of the jaw, 

 the Meckelian ossicle; anteriorly there is a small mental 

 bone. The palatoquadrate plus the hyomandibula and 

 symplectic form the suspensorium for the lower jaw. The 

 hyomandibula is bound to the metapterygoid and to the 

 symplectic, and also articulates above with the cranium. 

 The operculum is supported by a large opercle, a subo- 

 percle, and an interopercle. A series of branchiostegal rays 

 continue the opercular flap into the gular area. An anterior 

 medial gular occurs in some teleosts {Elops). 



The endocranium is difficult to understand because of 

 the overlapping and interdigitating of bones. In the salmon 

 (Figure 5-2) the bones are partly endochondral, joined by 

 synchondroses, whereas in the cod or perch they are largely 

 perichondral with overlapping sutures, synchondroses, or 

 combinations of these. There is usually a more or less con- 

 tinuous chondrocranium within and between these bones. 

 The occipital series is like that of the higher forms. There 

 is a large prootic ossification in the otic capsule and vari- 

 able smaller centers idenified as the epiotic and opisthotic. 

 In the region of the opisthotic there is a dermal bone, the 

 intercalare, which serves for the ligamentous attachment of 

 the pectoral girdle. The intertemporal and supratemporota- 

 bular have perichondral extensions on the otic capsule, the 

 sphenotic and pterotic. The sphenotie bears a hyomandi- 

 bular facet. A small strut of bone dividing the anterior 

 opening of the myodome in some fishes is called the 

 basisphenoid. The orbitosphenoid is a single or a two- 

 parted ossification in the orbit wall. Anteriorly there are 

 mesethmoid and lateral ethmoid ossifications. Two sclero- 

 tic plates are present in the eye of the salmon. 



There is a lateral commissure forming the posterior mar- 

 gin of the orbit and buttressing the sphenotic. Inside this 

 commissure lies the lateral canal or trigeminal-facial canal or 

 chamber, into which open separate trigeminal and facial 

 foramina. The geniculate ganglion of the seventh and the 

 Gasserian ganglion of the fifth nerve fill much of this cham- 

 ber. The cod lacks a lateral commissure. 



106 • THE HEAD SKELETON OF FISHES 



