192 PISCES. 



nus, Salmo, and Cobitis. The bones called nasal bones and infra- 

 orbital, are probably bones appertaining specially to the dermo- 

 skeleton, and are, therefore, improperly so termed. The inferior 

 maxilla invariably consists, upon either side, of at least two pieces, 

 of which the anterior is usually blended with that of the opposite 

 side to form a firm arch, and supports the teeth, whence it is called 

 the dental piece ; the posterior or articular piece articulates by gin- 

 glymus with the os quadratum. Usually, though not always, a 

 third bone, the angular piece, is found lying behind and beneath the 

 articular ; and more rarely a fourth, or complementary piece, is super- 

 added, which lies in the direction inward between the dental and 

 articular piece. Six pieces are rarely met with as in the genus 

 Lepidosteus, where the structure of the lower jaw reminds us of that 

 in the Reptilia, as the Crocodile. Occasionally a very considerable 

 gap remains between the dental and articular piece, e. g. in Zeus, 

 Pleuronectes maximus. The asymmetrical condition of the bones 

 of the cranium in the Plaice is extended also to those of the face, 

 but slightly to the lower jaw. 



Many Fishes exhibit greater varieties of cranium than those al- 

 ready mentioned, as is the case, for example, in Uranoscopus, Lepi- 

 doleprus, Lophius, Chironectes ; yet the description already given is 

 applicable in general to the Soft and Spiny-finned Fishes. The 

 genera Centriscus, Polyodon, Lepidosteus, Polypterus, &c., with the 

 Syngathi and Hippocampi, exhibit greater anomalies, not only in 

 the structure of their skull, but in the rest of the skeleton. 



As concerns the Vertebral Column of the Osseous Fishes, it con- 

 sists properly only of thoracic and caudal vertebrae, the first verte- 

 brae supporting ribs as well as the others, so that the cervical series 

 is wanting. The number of vertebrae is very various : in the elon- 

 gated Fishes, as the Eel, and others of that kind, e. g. Sphagebran- 

 chus, it exceeds 100 ; in Trichiurus lepturus above 150 ; in Gymnotus 

 aud Ophisurus above 200 ; in others only 20 30, as in Balistes. 



The bodies of the vertebrae in Fishes are well characterized by the 

 deep grooves upon their sides, and which penetrate so far as to per- 

 forate the latter, so that they present a series of apertures, as in the 

 Shad, Silurus glanis. Their anterior and posterior surfaces, where 

 the bodies unite to each other, exhibit a conical depression. In this 

 way a double infundibuliform cavity is formed, similar to that in the 

 Cartilaginous Fishes, between two vertebrae, and is filled up with a 

 gelatinous fluid which is found even in the centre of the vertebral 

 body. This fluid is enclosed in a membrane forming a kind of sac 



