116 ANATOMY OF VERTEBRATES. 



the Cartilaginous Fishes, however, it is articulated by means of a 

 pedicle with the orbitosphenoid. The osseous cavity or ' orbit ' 

 lodging the eyeball is formed by the presphenoid, orbitosphenoid, 

 frontal 11, postfrontal 4, prefrontal 14, and palatine 20, bones: it 

 opens widely outwards, where it is, often, further circumscribed 

 by the chain of suborbital scale-bones below, and, but less fre- 

 quently, by a superorbital bone above. The bony orbits in most 

 fishes communicate freely together, or rather with that narrow 

 prolongation of the cranial cavity lodging the olfactory crura : 

 but, in many Malacopteri, e. g. the Shads and Erythrinus, the 

 Citharinus and Hydrocyon, the Synbranchus, and the genus 

 Cyprinus, fig. 83, an osseous septum, is, divides the orbits. In 

 the Amia, Lepidosteus and Polypterus the orbits are divided 

 by a double septum, forming the proper walls of the olfactory 

 prolongation of the cranium, as is the case in the Batrachia. 



The olfactory capsules, or turhinals, fig. 81, 19, are lodged in a 

 cavity called ' nasal,' bounded by a variable number of bones, of 

 which the vomer, ib. 13, the prefrontals, ib. 14, and the nasals, ib. 

 15, are the most constant : in many bony fishes the nasal chamber 

 is closed behind by cartilage, which partly forms the interorbital 

 septum ; but in which, in some species, a slender symmetrical 

 bifurcate (Perch) or subquadrate ossicle is developed ; in the 

 Cyprinoid (fig. 83, is) and Siluroid Fishes, it articulates below to 

 the presphenoid, behind and above to the orbitosphenoids, .and 

 above and before to the frontals and prefrontals, forming the chief 

 part of the interorbital septum. The capsules of the terminal 

 pituitary expansion of the organ of smell are cartilaginous in the 

 Plagiostomes, Chimaeroids, in most Ganoids, and in the Lepido- 

 siren. They form a single tube, with interrupted cartilaginous 

 parietes, like a trachea, in several of the Cyclostomes. The tur- 

 binals are developed for the more immediate support of each ol- 

 factory capsule, in osseous fishes ; they are generally thin, more or 

 less elongated, and coiled scales ; situated at the sides of the nasal 

 bone and of the ascending processes of the premaxillaries ; usually 

 free, but in the Gurnards articulated with the prefrontals and 

 nasal, and in the Cock-fish (Argyreiosas) suspended above the nasal 

 bone, from the anterior prominence of the frontal spine. 



The palato-maxillary arch, fig. 81, 20,21,22, h, presents a simple 

 and intelligible condition in the Lepidosiren and Plagiostomous 

 fishes ; in all it is completed or closed at one point only, viz., where 

 the premaxillaries meet or coalesce, fig. 67, 22. The palatine bones 

 are the piers of this inverted arch, and their points of suspension 

 are their attachments to the prefrontals, the vomerine, and the 



