132 



THE ANATOMY OF YERTEBKATED ANIMALS. 



tebrse, and bear the fin-rays of the anal, and, in part, of the 

 caudal fin. 



The Teleostei differ very much in the extent to which the 

 primordial cranium persists throug-hout life. Sometimes, as 

 in the Pike (Figs. 44 and 45), it grows with the growth of the 



A 



a;s. J3S Fro. 



Fig. 44. — The cartilaginous cranium of the Pike {Esox Ivcius^, with its intrinsic ossifica- 

 tions; viewed. A, from above; B, from below; C, from the left, side: iV, N^ nasai fossa?; 

 /. Cr, interorbital septum; a, groove for the median ridge of the parasphenoid ; h^ canal 

 for the orbital muscles. Sq., wrongly so marked, is the Ftcrotic. V. and VIII. mark 

 the exits of the fiith and pneumogastric nerves ; 3, 3, small ossifications of the rostrum. 



fish, and only becomes partially ossified ; in other cases it al- 

 most disappears. A basi-occipital {JB. 0.), ex-occipital (E. 0.), 

 and supra-occipital {/S. 0.) bone are developed in it, and form a 

 complete occipital segment. The proper basi-sphenoid {JBS) 

 bone is always a very small, and usually somewhat Y-shaped, 

 bone. The alisphcnoids {AS.) sometimes are and sometimes 

 are not developed. The presphenoidal and orbitosphenoidal 

 regions commonly, but not always, remain unossified. 



In most osseous fishes, the base of the skull in front of the 

 '")asisphenoid is greatly compressed from side to side, and 



