78 



COMPARATIVE ANATOMY 



of the bony Ganoids, as is best seen by a comparison of the 

 Siluroids with Amia. On the other hand, no relations with the 



Amphibia are observable, 

 and we must consider the 

 whole group of the bony 

 Fishes as a side branch of 

 the piscine phylum. 



Much of the cartilagin- 

 ous primordial skull persists 

 in most Teleostei ; the 

 cranial cavity may either 

 reach between the eyes as 

 far as the ethmoid al region, 

 or it may become narrowed 

 and arrested in the orbital 

 region (Fig. 50, C), in 

 which ali-, orbito-, and 

 basi-sphenoid ossifications 

 may occur (Fig. 61). The 

 olfactory organs, as in most 

 other Fishes, consist of two 

 sacs lying in the cartilage of 

 the ethmoidal region. 



The palatoquadrate bar 

 becomes differentiated into 

 a row of bony plates 

 the quadrate, meso- and 

 metapterygoid, pterygoid, 

 and palatine. The audi- 

 tory capsule ossifies from 

 five centres (see p. 72), 

 and in the occipital region, 

 as well as on the dor- 

 sal surface of the skull, 

 numerous bones are de- 

 Pmx, premaxilla ; Na, external nostril ; N t veloped, for details of which 



nasal; Sb, Sb L , anterior and posterior the reader is referred to 



suborbital ; Orb, orbit ; M, maxilla ; 



ftp, spiracular bones ; PO, preopercu- 



lum (?) ; SO, suboperculum ; Op, oper- 



culum ; F, frontal ; P, parietal ; a, b, 



c, d, supraoccipital shields. The two 



arrows pointing downwards under the 



spiracular shields show the position of 



the openings of the spiracles on to the 



outer surface of the skull. 



FIG. 59. SKULL OF Polypterus bichir FROM 

 THE DORSAL SIDE. 



Figs. 60 and 61. 



In many Teleosts a canal, 

 lying in the axis of the base of 

 the skull, encloses the eye- 

 muscles, and opens on either 

 side into the orbit. 



All the bones bounding the oral cavity, viz., the vomer, the 

 parasphenoid, the premaxilla, and the maxilla, may bear teeth. 

 The maxilla, however, is usually edentulous, and both it and the 



