100 LECTURE V. 



from which the palatine bone is suspended.* In the MurcencB, also, 

 the prefrontals are plainly confluent with the nasal bone, and form 

 the well-marked articular surfaces for the palato-maxillarj bone. In 

 some fishes a process of the prefrontal circumscribes the foramen by 

 which the olfactory nerve finally emerges from the anterior pro- 

 longation of the cranio-vertebral canal. In the Carp the olfactory 

 nerve traverses a deep notch on the inner side of the prefrontal 

 (yfig. 35. 14). In the Cod the palatine arch is chiefly but not wholly 

 suspended to the prefrontals. The right prefrontal is the smallest in 

 the unsymmetrical skulls of the flat-fishes. 



The nasal hone (spine of the rhinencephalic arch, figs. 30. and 

 34. 15) is usually single, and terminates forwards in a thick obtuse 

 extremity. In some fishes, as the Sahnomd<s, the nasal is broad, 

 but not deep : in Istiophorus it is long and narrow : in the Dis- 

 coboles and Lophobranchii it is a short vertical compressed plate : it 

 is altogether absent in the Lophius, or is represented here, as in the 

 Diodon, by a fibrous membrane, retaining the primitive histological 

 condition of the skeleton. It is articulated above and behind to the 

 frontal and prefrontals, and below either directly or by a vertical 

 cartilage, as in the Cod, to the vomer. In the Flying Gurnard the 

 nasal has no immediate connection with the vomer ; but this is a 

 rare exception. In most fishes the nasal cavity is more completely 

 divided by the nasal bone into two distinct lateral fossas than in any 

 other class of Vertebrates. 



The backward prolongation of the usually cartilaginous, sometimes 

 membranous interorbital septum, in which one {Cyprinus, Gadus) or 

 more (Perca) osseous plates may be present, intervenes between and 

 more immediately supports the olfactory nerves. In the Salamandroid 

 Fishes the nasal is divided by a median suture. The horn-like pro- 

 jection from the fore part of the skull of the JVasens unicornis is 

 formed chiefiy by a process of the frontal bone, to the under part of 

 which a small nasal is articulated with a trifid anterior end, the 

 lateral divisions of which articulate with the premaxillaries, as in 

 Citharhms. The anterior end of the nasal is deepest in those Fishes 

 which have a small maxillary arch suspended from tlie cranial axis 

 by vertical palatines, and which have a large basi-cranial canal. 



The turbinate bones {fig. 30. 19), or osseous capsules of the nose, 

 are situated at the sides or above the nasal : the pre-maxillary and 

 the maxillary bones are usually attached to its extremity tlirougli the 



* In tlie Conger, Cuvier' recognises the prefrontals as persistent cartilages. 

 1 Op. cit. p. 2S5. 



