ICHTHYOLOGY. 



213 



Introduc- n:astoid ; but in the Perch, where it is more developed, he 

 tion. recognises it under its proper name. In the Cod it has a 

 Osteology, larger size, and the two otocranes are completely sepa- 

 '^'^^^•^ rated from each other. 



b. The optic capsule or sclerotic investment of the eye 

 is cartilaginous in the Chondropterygians and in semi- 

 osseous fishes, but in most osseous fishes it is bony. An 

 orbit for lodging the eye-ball is formed by the pre-sphenoid, 

 orbito-sphenoid, front;il, post-frontal, pre-frontal and pala- 

 tine bones ; its wide outer opening is oflen circumscribed 

 by tlie chain of sub-orbitals or scale-bones below, and less 

 frequently by one or more supra-orbitals above. In the 

 Shads, Erytlirimis, Citharinus, Hydroeijon, Cyprinus, and 

 many other Malacopteri, and in Si/nhrauc/ius, the orbits 

 are separated from one another by an osseous septum, but 

 in general the septum is incomplete or wanting ; in Lepi- 

 dostcus and Poli/pterus it is double. 



c. The nose-capsule is formed by the ethmoidal which 

 enters into the walls of the cranium, and the turhiiud which 

 belongs to the nose, other bones, as the vomer and nasal, 

 being accessaries. The whole capsule is cartilaginous in 

 cartilaginous and semi-osseous fishes, and the ethmoidal 

 part continues so in many osseous fishes. The cartilaginous 

 capsules and pituitary expansions are proportionally large 

 in the Chondropterygii and Lepidosiren, commmiicating 

 with each other in the latter by membranous slits ; but in 

 the higher fishes they form a pair. The turhinals in osse- 

 ous fishes are generally thin, more or less elongated, scales 

 situated at the sides of the nasal bone and ascending pro- 

 cesses of the pre-maxillaries. 



AA. The inferior or hamal arches of the cranial verte- 

 brae are essentially four in number in the osseous fishes, 

 and in most of these liave radiating appendages. A special 

 visceral system of bony arches, called " branchial," also 

 exists in fishes for the support and movement of the gills. 



4. Palato- maxillary arch. Of this inverted arch, the 

 palatine bones are the piers, and their points of sus])ension 

 are their attachments to the pre-fi'ontals, the vomerine, and 

 nasal bones. The arch is completed by the maxillary and 

 pre-maxillary bones, the symphysis of the latter forming 

 its apex. The palatine or pleurapophysis of the nasal 

 vertebra articulates at its peripheral extremity with the 

 maxillary, to which it affords a more or less moveable joint. 

 In the Parrot fishes and Diodons the articulation is analo- 

 gous to that of the mandible below, with the tympanic 

 pedicle. In the Salamandroid fishes it is a fixed suture. 

 In Mormyrus these ends of the palatines meet and imite 

 at the mesian line. In fig. 19, representing the jaws of 

 Alepisnurus, the palatines are seen to be strongly armed, 

 each of them having two pairs of tall lancet-shaped teeth, 

 one pair nearly imder the nostrils, the second pair not so 

 tall, further back, and closely followed by ten much shorter 

 ones. The maxillary or heemapophysis of the nasal verte- 

 bra lies between the palatine and pre-maxillarv. On the 

 extent to which these two bones enter severally into the 

 orifice of the mouth, and on their dcntiftrous or eden- 

 tulous conditions, many divisions of fishes made by ichthy- 

 ologists are mainly fovmded. In the Salmonoids the max- 

 illary joins to the lower end of the pre-maxillary, forming, 



'■^^ii^imMm^ 



Fig. 17. 

 Coilia Plaijfalrii, one of the ClvpciJa; of tlie China seas. 



together with it, the upper half of the border of the mouth, 



and it siipports teeth. The same form prevails with the Introduc- 



Clupeoids. In Thrissa and Coilia of this family the *'""• 



pre-maxillary is very small, and the large dentiferous max- Osteology. 



illary is prolonged beyond the corner of the mouth (fig. 17). ^"^ ^/— ^ 



In the Plectnynathi the two bones coalesce. In Lepidos- 



teus these bones also form a single dentiferous arch, but 



they are subdivided into many pieces, a condition which 



seems to have prevailed with the ancient Salamandroid 



fishes. It is dentiferous and largely developed in Polyptertis, 



but very diminutive in the Sihnoids, and wanting in the 



3Iur(enid(e. 



The pre-maxillary, or the haemal spine of the nasal ver- 

 tebra, is more commonly directed transversely than longitu- 

 dinally. Its nasal branch, or pedicle, is of unusual length in 

 fishes with protractile snouts, such as the Menida, Zeida, 



Fig. IS. 

 EmmeUclithys nitidus{ErythHchthijs Schlegel), from Western Australia. 



Epihtdus, Emmelichthys, and others. Commonly, its labial 

 border is beset with teeth ; and in many groups of fish 

 it forms, with its fellow and the mandible, the whole mar- 

 gin of the mouth, the maxillaries in that case lying in folds 

 of skin. 'I'his extension of the pre-maxillary is well shown 

 in the Alepisaurus, a predaceous Sphyrcenoid ; there it is 



Fig. 19. 

 Alepisaurlts. one of the Spln/ra-nid(e, a piedacious familj-, nearly allied to the 

 Sconiberoids. Tho upper" boi-der of the mouth is formed wiinily by the pre- 

 maxillaries, which arc armed with small teeth. Valoneieuues, who knew 

 the fish only from a drawing, places it among the Satmonida;, 



closely set by a series of small teeth (fig. 19). The small 

 bony piece above the maxillary in the Trout, Herring, and 

 Pike, seems to belong to the series of mucous or scale bones. 



The dirergiiiij appendage of the palato-maxillary arch 

 consists of the pterygoid and entopterygoid bones, which 

 are the less constant parts of the arch. They are connate 

 with the palatine in most Salmonoids and Eels, while Mu- 

 r£ena wants the entopterygoid, and its pterygoid is discon- 

 nected tiom the maxillary arch. Most fishes, however, have 

 both bones. 



3. The tympano-mandihular arch has the true inverted 

 or ha'mal character, its apex formed by the epi-tymp((Hics 

 or pleurapophyses of the frontal vertebra hanging down- 

 wards below the vertebral axis of the skull. In most fislies, 

 its lower end is bifid, and supports two inverted arches, 

 the mandibular and the hyoideaii. The meso-ti/ni panic is 

 articulated above to the epi-tympanic and pre-opercular, 

 anteriorly to the pre-tympanic, and by its lower end to the 



