MORPHOLOGY OF TELE0STI5AN HlilAD SKIilLETON. 549 



The hyoniandibular and symplectic are widely separated 

 from one another by a broad area of cartilage. As a whole, 

 the former presents a striking contrast to the simple liyoman- 

 dibular of the salmon, and seems to be made up of four 

 radii connected by more or less extensive laminee of bone. 

 The two uppermost end in cartilaginous articular heads [hym.") 

 which fit into facets described above. The edge of the 

 lamina between them takes no part in the articulation, so tliat 

 during the development of this region there is a complete 

 transition from the long simple articulation present in the 

 adult salmon to the double articulation Avitli two rounded 

 heads. The pike has the double-headed articulation ; the 

 heads, however, are not rounded. In Belone this articulation 

 is intermediate between that of the salmon and the pike. 

 The anterior lower radius now passes obliquely forward, as in 

 pike and Belone. 



The hyomaudibular nerve has the same course as in the 

 previous stage. In the cod it passes in front of the main 

 radius, and thus seems to suggest that even within the 

 Tcleostei this nerve does not bear a constant relationship 

 to the hyomaudibular — a conclusion to which Pollard (94, 

 p. 24) was led by a comparison of its position in Ganoids. 



The symplectic (sym.) is still nearly twice the length of 

 the hyomaudibular — itself a long bone, — and thus presents a 

 striking contrast to this in other forms, for both in pike 

 and Alepocephalus it is shorter than the hyomaudibular, 

 and in the salmon it is but an insignificant appendage of 

 this. Belone offers an intermediate condition, for in it the 

 bones are of equal length. In the stickleback its extremity 

 remains cartilaginous, and is almost completely enclosed by 

 the quadrate aud its laminar outgi-owth. 



The metapterygoid is unaltered except for the fact that in 

 surface view the original shape and extent of the cartilage, 

 now largely ossified, is disguised by the great laminar 

 extensions of bone dorsally and veutrally. Nevertheless, 

 the reduced condition of that cartilage is more than indicated 

 by its width at the point where it enters the ossification. In 



