270 



TELEOSTOMI 



is invaded by the prefrontal (lateral ethmoid), originally a superficial 

 bone, which may sink below the surface in higher forms (p. 345). 

 A median ethmoid may grow into the cartilaginous internasal 

 septum from above, and sometimes the vomer also from below. 

 Little paired septomaxillaries (Fig. 237) may occasionally be found 

 in the nasal capsule near the articulation of the maxilla (Parker 

 [319], Bruch [65], Sagemehl [379], etc.). 



Accompanying the great development of the bones of the skull 

 is a corresponding reduction of the chondrocranium (Parker [319], 

 Swinnerton [431], Gaupp [151a]). The cartilaginous walls of the 

 brain-case are, as a rule, very incomplete. A large fontanelle is 

 found above, limited behind by an arch, the tectum synoticum, 



Fig. 239. 



Amia calva, I.. Skeleton of the left jaws and liyoid arch, from which the dermal bones of 

 the lower jaw have l>e<-n removed. (AfterAllis, slightly modified.) The cartilage is dotted. a,j>, 

 endochondral palatine; b, process articulating with proof ic ; c.p, coronoid process; enpt, 

 endopterygoid ; eph, epihyal : ept, ectopterygoid : h, hyomandibular : h.<*, its articular head ; 

 Mi, hypohyal; i.r, ventral segment of ceratohyal ; /, ligament; m, Meckel's cartilage; m.m, 

 inento-Meekelian ; tnp, metapterygoid ; >i, foramen for hyomandibular nerve ; o.a, articular 

 head for opercular ; ;>, palatine' (dermal) ; pg, palato-pterygoid cartilage ; q, quadrate ; sy, 

 symplectic ; it.c, upper segment of ceratohyal. 



between the auditory capsules. A hypophysial space below 

 separates the two trabeculae, which fuse in front to form the 

 nasal and antorbital cartilage, but hardly contribute at all to the 

 closure of the side walls (Fig. 58). 



The attachment of the jaws is always of the hyostylic type. 

 The hyomandibular is large, and supports the quadrate some 

 distance from the cranium (Figs. 239, 302, 456). At its anterior 

 end the palato-quadrate bar has a palatine bone ; it often bears teeth 

 and may be subdivided into an endochondral and a dermal element 

 (Amia, Allis [10], Fig. 239 ; Lepidosteus, van Wijhe [494]). Usually 

 it articulates with both the ethmoid region of the skull and the 

 maxilla. There follow behind a dermal ectopterygoid (pterygoid) 



